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Maths68 answered: 1474 problems
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Functions/516389: For each function, find f(-2), f(-1/2), f(3), and f(7).
1. f(x)= -1/3x + 1
1 solutions

Answer 344355 by Maths68(1474) About Me  on 2011-10-17 13:21:08 (Show Source):
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For each function, find f(-2), f(-1/2), f(3), and f(7).

f(x)= -1/3x + 1
f(-2)=-1/3(-2)+1
f(-2)=1/6+1
f(-2)=(1+6)/6
f(-2)=7/6


f(x)= -1/3x + 1
f(-1/2)=-1/(3(1/-2))+1
f(-1/2)=-1/(3/-2)+1
f(-1/2)=2/3+1
f(-1/2)=(2+3)/3
f(-1/2)=5/3


f(x)= -1/3x + 1
f(3)=-1/3(3)+1
f(3)=-1/9+1
f(3)=(-1+9)/9
f(3)=8/9



f(x)= -1/3x + 1
f(7)=-1/3(7)+1
f(7)=-1/21+1
f(7)=(-1+21)/21
f(7)=20/21


test/516388: What number is 62% of 25
1 solutions

Answer 344354 by Maths68(1474) About Me  on 2011-10-17 13:11:44 (Show Source):
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What number is 62% of 25
=62% * 25
=62/100 * 25
=62/4
=15.5
15.5 is 62% of 25


Mixture_Word_Problems/516387: A metallurgist has one alloy containing 25% copper and another containing 62% copper. How many pounds of each alloy must he use to make 45 pounds of a third alloy containing 34% copper?
1 solutions

Answer 344353 by Maths68(1474) About Me  on 2011-10-17 13:09:29 (Show Source):
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Ally A
Amount = x
Concentration = 25%=0.25
================================================================================
Alloy B
Amount = 45-x pounds
Concentration = 62%=0.62
================================================================================
Resultant Alloy
Amount=45
Concentration=34%=0.34
================================================================================
(Amount of A * Concentration of A)+(Amount of B * Concentration of B) = (Amount of Resultant * Concentration of Resultant)
(x*0.25)+(45-x)(0.62)=(45)*0.34
0.25x+27.9-0.62x=15.3
-0.37x=15.3-27.9
-0.37x=-12.6
-0.37x/-0.37=-12.6/-0.37
x=34.05 pounds
============================
Ally A
Amount = 34.04 pounds
Concentration = 25%=0.25
================================================================================
Alloy B
Amount = 45-x=45-34.04=10.95 pounds
Concentration = 62%=0.62


Money_Word_Problems/516338: find the total cost of an engagement ring at 3240 including sale tax of 6.5%?
1 solutions

Answer 344352 by Maths68(1474) About Me  on 2011-10-17 12:52:51 (Show Source):
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find the total cost of an engagement ring at 3240 including sale tax of 6.5%?
6.5% of 3240 = 3240*6.5%=3240*(6.5/100)=3240*0.065=210.6
Total cost = 3240+210.6=3450.60


or
find 106.5% of 3240 = 3240*(106.5/100)=3240*1.065=3450.6


Mixture_Word_Problems/516357: a chemist has a 10 ml of a 30% acid solution. how many millilters of pure acid must be added to obtain a 50% solution?
1 solutions

Answer 344351 by Maths68(1474) About Me  on 2011-10-17 12:44:04 (Show Source):
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Soluton A
Amount = 10 ml
Concentration = 30%=0.3
================================================================================
Solution B
Amount = x ml
Concentration = 100%=1 (Pure acid)
================================================================================
Resultant Solution
Amount=10+x ml
Concentration=50%=0.5
================================================================================
(Amount of A * Concentration of A)+(Amount of B * Concentration of B) = (Amount of Resultant * Concentration of Resultant)
(10*0.3)+(x*1)=(10+x)*0.50
3+x=5+0.5x
x-0.5x=5-3
0.5x=2
0.5x/0.5=2/0.5
x=4 ml
================================================================================
10 ml of a 30% acid solution and 4 ml of pure acid must be mixed to obtain 14 ml of 50% solution


Linear-equations/516377: Not sure how to find the slope of the line joining (3, 12) and (15, -2)as a fraction in the simplest form.
1 solutions

Answer 344350 by Maths68(1474) About Me  on 2011-10-17 12:29:52 (Show Source):
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(3, 12) and (15, -2)
Slope of line = Change in y / change in x
m=y2-y1/x2-x1
m=-2-12/15-3
m=-14/12
m=-7/6
Slope = -7/6


Linear-equations/516363: write an equation in slope-intercept form for a line that passes through the given point and is parallel to the given line
y=5x;(2,-1)
1 solutions

Answer 344349 by Maths68(1474) About Me  on 2011-10-17 12:24:55 (Show Source):
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Standard Form of Equation of the line:
y=mx+b
Given line
y=5x
Compare above equation with the standard form equation
Slope = m=5 and y-intercept = b=0
Since parallel lines have same slope so slope of the required line will be:-
m=5
Now we have a point(2,-1) and slope (5)of the line we can easily find required lines by putting these values in the equation of the straight line poin-slope form.
m=(y2-y1)/(x2-x1)
5=(y-(-1))/(x-2)
5=(y+1)/(x-2)
5(x-2)=y+1
5x-10=y+1
y+1=5x-10
y=5x-10-1
y=5x-11
Above equation is the required equation of the line that is parallel to y=5x and contains (2,-1)


Mixture_Word_Problems/516359: a chemist has two solutions of h2so4. one has 40% concentration and the other has a 25% concentration. how many liters of solution must be mixed to obtain 96 liters of a 27% solution
1 solutions

Answer 344347 by Maths68(1474) About Me  on 2011-10-17 12:10:12 (Show Source):
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Soluton A
Amount = x
Concentration = 40%=0.4
================================================================================
Solution B
Amount = 96-x liters
Concentration = 25%=0.25
================================================================================
Resultant Solution
Amount=96
Concentration=27%=0.27
================================================================================
(Amount of A * Concentration of A)+(Amount of B * Concentration of B) = (Amount of Resultant * Concentration of Resultant)
(x*0.4)+(96-x)(0.25)=(96)*0.27
0.4x+24-0.25x=25.92
0.15x=25.92-24
0.15x=1.92
0.15x/0.65=1.92/0.15
x=12.8 liters

================================================================================
Soluton A
Amount = x = 12.8 liters
Concentration = 40%=0.4
================================================================================
Solution B
Amount = 96-x=96-12.8=83.2 liters
Concentration = 25%=0.25
===============================================================================
12.8 liters of 40% concentration and 83.2 liters of 25% concentration solutoins must be mixed to obtain 96 liters of a 27% solution


Travel_Word_Problems/516340: Two buses leave Dallas at the same time and travel in opposite directions. One bus travels at 58 mph and the other travels at 52mph when will they be 363 miles apart?
1 solutions

Answer 344345 by Maths68(1474) About Me  on 2011-10-17 11:49:04 (Show Source):
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Bus A Data
==========
Speed = 58mph
Time=t hour
Distance Covered by Bus A=58*t
=============
Bus B Data
============
Speed = 52mph
Time=t hour
Distance covered by Bus B=52*t
Distance Covered by Bus A + Distance Covered by Bus B = Total Distnace apart
52t+58t=363
110t=363
110t/110=363/110
t=3.3 hour

They will be 363 miles apart after 3.3 hours or 3 hours 18 minutes.


Check
=============
Bus A Data
==========
Speed = 58mph
Time=3.3 hours
Distance Covered by Bus A=58*3.3=191.4 miles
Bus B Data
============
Speed = 52mph
Time=3.3 hours
Distance covered by Bus B=52*3.3 = 171.6 miles
Total Distance between two Buses = 191.4+171.6 = 363 miles



Travel_Word_Problems/516334: A car left seattle traveling 45mph. A second car left from the same place one hour later on the same road traveling 60mph. How long will it take the second car to catch up with the first car. Which of these is the correct second eqaution for the problem?
1 solutions

Answer 344341 by Maths68(1474) About Me  on 2011-10-17 11:22:35 (Show Source):
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A car left seattle traveling 45mph. A second car left from the same place one hour later on the same road traveling 60mph. How long will it take the second car to catch up with the first car. Which of these is the correct second eqaution for the problem?

Car A Data
==========
Speed = 45mph
Time = t hour
Distance covered = x miles
Distance = speed*time
x=45*t
x=45t.............(1)

Car B Data
==========
Speed = 60mph
Time =t-1(hour)
Distance covered = x
Distance = Speed * time
x=60*(t-1)

Both cars will cover same distance
45t=60*(t-1)
45t=60t-60
45t-60t=60
-15t=-60
-15t/-15=-60/-15
t=4 hours
Car A travel time 4 hours and Car B travel time 3 hours.
After 3 hours of leaving same place Car B will catch Car A
Check
========
Car A Data
==========
Speed = 45mph
Time = 4 hour
Distance covered = x miles
Distance = speed*time
x=45*4
x=180 miles
Car B Data
==========
Speed = 60mph
Time =t-1=4-1=3(hour)
Distance covered = x
Distance = Speed * time
x=60*3
x=180 miles


Proportions/516265: Two numbers are in ratio of 7:11. If 7 is added to each of the number, the ratio becomes 2:3. Find the numbers.
1 solutions

Answer 344313 by Maths68(1474) About Me  on 2011-10-17 05:27:28 (Show Source):
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Let x and y are two numbers

x:y=7:11
x/y=7/11
11x=7y
x=7y/11............(1)

(x+7):(y+7)=2:3
(x+7)/(y+7)=2/3
3(x+7)=2(y+7)
3x+21=2y+14
3x=2y+14-21
3x=2y-7............(2)
Put the value of x in (2) from (1)
3(7y/11)=2y-7
21y/11=2y-7
21y=11*(2y-7)
21y=22y-77
21y-22y=-77
-y=-77
y=77
Put the value of y in (1)
x=7y/11............(1)
x=7(77)/11
x=7*7
x=49


Numbers are 49 and 77


49/77=7/11=7:11
(49+7)/(77+7)=56/84=28/42=14/21=2/3=2:3


Graphs/516236: How do I solve 0.3x-0.2y=4 and 0.2x + 0.3y=29/19 using the elimination method?
1 solutions

Answer 344297 by Maths68(1474) About Me  on 2011-10-17 01:36:54 (Show Source):
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0.3x-0.2y=4...............(1)
0.2x + 0.3y=29/19.........(2)
Make above equations more simple
3x/10+2y/10=4
Multiply by 10 both sides of above equation
3x+2y=40.................(3)
2x/10+3y/10=29/19
Multiply by 10 both sides of above equation
2x+3y=290/19.............(4)
Multiply (3) by -2 and (4) by 3 and add the resultant equations
-6x-4y=-80
6x+9y=870/19
------------------
5y=870/19-80
5y=(870-1520)/19
5y=-650/19
5y/5=-650/19/5
y=-130/19
Put the value of y in (3)
3x+2y=40.................(3)
3x+2(-130/19)=40
3x-260/19=40
Multiply by 19 both sides
57x-260=760
57x=760+260
57x=1020
57x/57=1020/57
x=1020/57
x, y =1020/57,-130/19
Check
Put the values of x and y in (4)
2x+3y=290/19.............(4)
2(1020/57)+3(-130/19)=290/19
2040/57-390/19=290/19
(2040-1170)/57=290/19
870/57=290/19
290/19=290/19


Rectangles/516171: The length of a rectangle is 5 more than it's width. the perimeter is 9 times more then the width. what are the dimensions of the rectangle
1 solutions

Answer 344286 by Maths68(1474) About Me  on 2011-10-17 00:15:34 (Show Source):
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Length = l=w+5
Width = w=?
Perimeter = p = 9w
==============================
Perimeter of a Rectangle = length + length + width + width
Perimeter of a Rectangle =2 length +2 width
P = 2l + 2w
9w=2(w+5)+ 2w
9w=2w+10+2w
9w=4w+10
9w-4w=10
5w=10
5w/5=10/5
w=2
============================
Dimensions of the Rectangle
Length = l=w+5 = 2+5 =7
Width = w=2
Perimeter = p = 9w = 9*2=18



Linear-equations/516173: 4(2x-3)=-2(3x-8)
what is x?
1 solutions

Answer 344263 by Maths68(1474) About Me  on 2011-10-16 22:22:12 (Show Source):
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4(2x-3)=-2(3x-8)
8x-12=-6x+16
8x+6x=16+12
14x=28
14x/14=28/14
x=2
Check
4(2x-3)=-2(3x-8)
4(2(2)-3)=-2(3(2)x-8)
4(4-3)=-2(6-8)
4(1)=-2(-2)
4=4


Linear-equations/515775: Can you solve these problems by substitution?
1.)
x + 2y = -1
4x - 5y = 22
2.)
-3x + 7y = 14
2x - y = -13
1 solutions

Answer 344165 by Maths68(1474) About Me  on 2011-10-16 13:32:03 (Show Source):
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1.)
x + 2y = -1............(1)
4x - 5y = 22...........(2)
Multiply (1) by -4 and add to (2)
-4x-8y=4
4x-5y=22
-13y=26
-13y/-13=26/-13
y=-2
Put the value of y in (1)
x+2y=-1
x+2(-2)=-1
x-4=-1
x=-1+4
x=3
x,y = 3, -2
Check
Put the values of x and y in (1)
x + 2y = -1............(1)
3+2(-2)=-1
3-4=-1
-1=-1

2.)
-3x + 7y = 14 ..........(1)
2x - y = -13...........(2)
Multiply (2) by 7 and add to (2)
-3x + 7y = 14
14x - 7y = -91
--------------
11x=-77
11x/11=-77/11
x=-7
Put the value of x in (2)
2x - y = -13...........(2)
2(-7)-y=-13
-14-y=-13
-y=-13+14
-y=1
y=-1
x,y=-7,-1
Check
Put the values of x and y in (2)
2(-7) - (-1) = -13
-14 + 1 = -13
-13=-13



Rectangles/515791: The length of a rectangle is 2ft longer than its width.
If the perimeter of the rectangle is 40ft , find its area.
1 solutions

Answer 344163 by Maths68(1474) About Me  on 2011-10-16 13:13:02 (Show Source):
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Perimeter = P = 40 ft
Width = w
Length = w+2
Perimeter = 2l +2w
40=2(w+2)+2w
40=2w+4+2w
40=4w+4
40-4=4w
36=4w
36/4=4w/4
9=w
w=9
Perimeter = P = 40 ft
Width = w = 9
Length = w+2 = 9+2 = 11


Linear-equations/515785: Solve this problem through substitution:
x + y = 6
x - y = -2
1 solutions

Answer 344161 by Maths68(1474) About Me  on 2011-10-16 13:08:34 (Show Source):
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x + y = 6 ...........(1)
x - y = -2 ..........(2)
Add (1) and (2)
x + y = 6
x - y = -2
------------
2x=4
2x/2=4/2
x=2
Put the value of x in (1)
x + y = 6 ...........(1)
2+y=6
y=6-2
y=4
x,y=2,4


Age_Word_Problems/515764: A man is 4 times as old as his son. Five years ago, the sum of their ages was 30.Form an equation in a variable of your choice and hence calculate their present ages.
1 solutions

Answer 344156 by Maths68(1474) About Me  on 2011-10-16 12:43:41 (Show Source):
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A man is 4 times as old as his son. Five years ago, the sum of their ages was 30.Form an equation in a variable of your choice and hence calculate their present ages.
Let
Present age of Man = m
Present age of Son = s


Man is 4 times as old as his son.
m=4s..........(1)
Five years ago,
m-5=s-5
the sum of their ages was 30
(m-5)+(s-5)=30
m-5+s-5=30
m+s-10=30
m+s=30+10
m+s=40.............(2)
Put the value of m from (1) to (2)
4s+s=40
5s=40
5s/5=40/5
s=8
Put the value of s in (1)
m=4s
m=4(8)
m=32
Present age of Man = m = 32 years old
Present age of Son = s = 8 years old


expressions/515766: Can you show me how to solve this problem: 6y-2+2y=14
1 solutions

Answer 344153 by Maths68(1474) About Me  on 2011-10-16 12:38:06 (Show Source):
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6y-2+2y=14
8y-2=14
8y=14+2
8y=16
8y/8=16/8
y=2


Numbers_Word_Problems/515765: when 4 is added to a number and the result is divided by 3, the answer is 5. Find the number.
1 solutions

Answer 344151 by Maths68(1474) About Me  on 2011-10-16 12:33:56 (Show Source):
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Let
Number = x
(4+x)/3=5
(4+x)=5*3
4+x=15
x=15-4
x=11
Number is 11


Linear_Algebra/515747: Saidhari bought a toaster oven for 90 dollars. this price was 1/4 off the list price. what was the list price.
1 solutions

Answer 344150 by Maths68(1474) About Me  on 2011-10-16 12:31:25 (Show Source):
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Saidhari bought a toaster oven for 90 dollars. this price was 1/4 off the list price. what was the list price.
List price = x
1/4 of list price = x(1/4)=x/4
List pirce - discount = Discounted price
x-x/4=90
4x-x/4=90
3x/4=90
x=90*4/3
x=30*4
x=120
List price = $120


Linear-systems/515732: solve for r, 36r^2-1=0

1 solutions

Answer 344142 by Maths68(1474) About Me  on 2011-10-16 11:35:20 (Show Source):
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solve for r, 36r^2-1=0
36r^2-1=0
(6r)^2-(1)^2=0
(6r-1)(6r+1)=0
(6r-1)=0 or(6r+1)=0
6r=1 or6r=-1
r=1/6 or r=-1/6


Expressions-with-variables/515716: solve for x
ax-x=c
Here is what I've come up with... x=c/a-1
Is this correct?
1 solutions

Answer 344140 by Maths68(1474) About Me  on 2011-10-16 11:30:46 (Show Source):
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You are right well done!
Keep it up!!
solve for x
ax-x=c
x(a-1)=c
x(a-1)/(a-1)=c/(a-1)
cancel out (a-1) from left hand side of the equation
x=c/(a-1)


Linear_Equations_And_Systems_Word_Problems/515724: sara and jim both decided to save some money each week. sara has already saved 4100, and she plans to save $10 a week. jim plans to save $15 a week. in how many weeks will jim and sara have saved the same amount?
1 solutions

Answer 344138 by Maths68(1474) About Me  on 2011-10-16 11:21:26 (Show Source):
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Let it takes x weeks to equalize their savings.
15*x=4100+10*x
15x=4100+10x
15x-10x=4100
5x=4100
5x/5=4100/5
x=820
After 820 weeks or 205 months or 17 years, one month and one week !!!!!


Expressions-with-variables/515722: Solve the equation for y. Then find the value for y for each value x.
6x=7-4y; x= -2, -1, 0
1 solutions

Answer 344137 by Maths68(1474) About Me  on 2011-10-16 11:09:55 (Show Source):
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6x=7-4y
4y=-6x+7
4y/4=(-6x+7)/4
y=(-6x+7)/4
=====================
x=-2
y=(-6(-2)+7)/4
y=(12+7)/4
y=19/4
===================
x=-1
y=(-6(-1)+7)/4
y=(6+7)/4
y=13/4
=================
x=0
y=(-6(0)+7)/4
y=7/4


Expressions-with-variables/515719: Solve the equation for y. Then find the value for y for each value x.
4x=3y-7; x= a, 5, 6
1 solutions

Answer 344136 by Maths68(1474) About Me  on 2011-10-16 11:02:57 (Show Source):
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4x=3y-7; x= a, 5, 6
4x=3y-7
rearrange above equation
3y-7=4x
3y=4x+7
3y/3=(4x+7)/3
y=(4x+7)/3
===========================
Now
x=a
y=(4a+7)/3
==========================
x=5
y=(4(5)+7)/3
y=(20+7)/3
y=27/3
y=9
==========================
x=6
y=(4(6)+7)/3
y=(24+7)/3
y=24/3+(7/3)
y=8+(7/3)


Age_Word_Problems/515636: two years ago father was 3 times as old as his son and 2 year hence,twice his age will be equal to 5 times that of his son find present age ?
1 solutions

Answer 344102 by Maths68(1474) About Me  on 2011-10-16 02:39:55 (Show Source):
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Let
Present age of Father = f
Present age of Son = s

Two years ago
f-2=s-2
Father was 3 times as old as his son
f-2=3(s-2)
f-2=3s-6
f=3s-6+2
f=3s-4............(1)
and 2 year hence,
f+2=s+2
then twice his age will be equal to 5 times that of his son
2(f+2)=5(s+2)
2f+4=5s+10
2f=5s+10-4
2f=5s+6.............(2)
Put the value of f in (2) from (1)
2(3s-4)=5s+6
6s-8=5s+6
6s-5s=6+8
s=14
Put the value of s in (1)
f=3s-4............(1)
f=3(14)-4
f=42-4
f=38
Present age of Father = f = 38 years old
Present age of Son = s = 14 years old


Age_Word_Problems/515634: Rico is twice old as Ryan.In four years,Rico's age will be three times as Ryan's age is six years ago.How old are they now?
1 solutions

Answer 344101 by Maths68(1474) About Me  on 2011-10-16 02:29:14 (Show Source):
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Let
Present age of Rico = r
Present age of Ryan = y


Rico is twice old as Ryan
r=2y........(1)
In four years,Rico's age will be three times as Ryan's age is six years ago
Rico age in four years = r+4
Ryan age six years ago = y-6
r+4=3(y-6)
r+4=3y-18
r=3y-18-4
r=3y-22.............(2)
Put the value of r in (2) from (1)
2y=3y-22
2y-3y=-22
-y=-22
Multiply by -1 both sides
y=22
Put the value of y in (1)
r=2y
r=2(22)
r=44
Present age of Rico = r = 44 years old
Present age of Ryan = y = 22 years old
Six years ago Ryan was = 22-6 = 16
In four years Rico will be = 44+4 = 48 (which is 3 times of 16)


Age_Word_Problems/513251: In 36 years, Anna will be five times as old as she is today. How old is Anna?
1 solutions

Answer 344100 by Maths68(1474) About Me  on 2011-10-16 02:17:35 (Show Source):
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Let
Present age of Anna = a
In 36 years
a+36=5a
a+36=5a
a-5a=-36
-4a=-36
-4a/-4=-36/-4
a=9
Anna is 9 years old now.
In 36 years she will be =(36+9)= 45 (which is 5 times of 9)



Age_Word_Problems/513480: selma is now 3 times as old as joyce. four years ago, selma was 4 times as old as joyce was then. find their present ages.

1 solutions

Answer 344099 by Maths68(1474) About Me  on 2011-10-16 02:08:10 (Show Source):
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Let
Present age of Selma = s
Present age of Joyce = j

selma is now 3 times as old as joyce
s=3j........(1)
Four years ago,
s-4=j-4
then
Selma was 4 times as old as joyce
s-4=4(j-4)
s-4=4j-16
s=4j-16+4
s=4j-12.............(2)
Put the value of s in (2) from (1)
3j=4j-12
3j-4j=-12
-j=-12
Multiply by -1 both sides
j=12
Put the value of j in (1)
s=3j
s=3(12)
s=36
Present age of Selma = s = 36 years old
Present age of Joyce = j = 12 years old


Age_Word_Problems/513424: In 1985 Maria was three times as old as Sue. Five years earlier, the sum of their ages was eighteen. In what year was Maria born?
1 solutions

Answer 344098 by Maths68(1474) About Me  on 2011-10-16 02:00:48 (Show Source):
You can put this solution on YOUR website!

In 1985
========
Maria was = m years old
Sue was = s years old
Maria was three times as old as Sue
m=3s........(1)
1980
====
Five years earlier
(s-5)+(m-5)=18
s-5+m-5=18
s+m-10=18
s+m=18+10
s+m=28.......(2)
=============================================================================
Put the value of m from (1) to (2)
s+(3s)=28
s+3s=28
4s=28
4s/4=28/4
s=7
Put the value of s in (1)
m=3s
m=3(7)
m=21
In 1985
Maria was = m = 21 years old
Sue was = s = 7 = years old
Maira was born in = 1985 - 21 = 1964