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drk answered: 1901 problems
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Numbers_Word_Problems/258042: Two numbers have the sum of -6 and a product of -16. Find the integers.
1 solutions

Answer 189886 by drk(1908) About Me  on 2010-01-18 14:05:47 (Show Source):
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Let x and Y be the numbers. From the given information, we get
(i) X+%2B+Y+=+-6
(ii) X%2AY+=+-16
step 1 - solve for X in (i) to get
(iii) X+=+-6+-+Y
step 2 - substitute (iii) into (ii) to get
(iv) %28-6-Y%29%28Y%29+=+-16
expand (iv) to get
(v) -Y%5E2+-+6Y+=+-16
set = 0 to get
(vi) -Y%5E2+-6Y+%2B+16+=+0
divide by -1 and factor to get
(vii) %28Y-2%29%28Y%2B8%29=0
solve to get
Y = 2, Y = -8. We have two answers in x,y form as
(-8,2) and (2,-8)


Permutations/258040: in how many ways can 3 cards from a deck of 52 by laid in a row face up?
1 solutions

Answer 189885 by drk(1908) About Me  on 2010-01-18 14:01:36 (Show Source):
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We have a combination problem. We want 3 face up , but also we want the rest, 49, face down, so we can say
52c3 = 22100


Equations/258036: How would you write this in standard form using integers? y=2/3x-25/3. Thanks so much!
1 solutions

Answer 189884 by drk(1908) About Me  on 2010-01-18 13:59:25 (Show Source):
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We are given
(i) y=%282%2F3%29x-25%2F3
standard form requires two things
(1) no fractions
(2) x and y on the same side
--
step 1 - multiply (i) by 3 to get
(ii) 3y+=+2x+-+25
step 2 - subtract 2x to get
-2x+%2B+3y+=+-+25
at this point some teacher require positive x's, sop we could write
2x++-+3y+=+25


Linear-equations/258033: slope and the vertical and horizontal intercept
y=5x+2 can you show me the work so i know how to do this please thank you very much.
1 solutions

Answer 189883 by drk(1908) About Me  on 2010-01-18 13:57:01 (Show Source):
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We start with
(i) y+=+5x%2B2
This is similar to
(ii) y+=+mx+%2B+b
matching up the 2 we get
slope = m = 5.
--
If we were to graph this, it would be a line.
vertical intercept = do you mean x-intercept?
horizontal intercept = do you mean y-intercept?
--
X-intercept is when y = 0. If y = 0, then
0+=+5x+%2B+2
-2+=+5x
%28-2%2F5%29+=+x
--
Y-intercept is when x = 0. If x = 0, then
y+=+5%2A0+%2B+2
y+=+2


Linear_Equations_And_Systems_Word_Problems/258029: Janet invested $27,000, part at 15% and part at 9%. If the total interest at the end of the year is $3,390, how much did she invest at 15%?
1 solutions

Answer 189879 by drk(1908) About Me  on 2010-01-18 13:51:31 (Show Source):
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This question is modeled after the I = prt question. IN this case however, we have two investments. So we can write
I = prt + prt
based on the given information, we get
(i) 3390+=+x%28.15%29%281%29+%2B+%2827000-x%29%28.09%29%281%29
simplifying (i) , we get
(ii) 3390+=+.15x+%2B+2430+-.09x
and then
(iii) 3390+=+.06x+%2B+2430
subtracting, we get
(iv) 1060+=+.06x
and dividing, we get
x = $11,777.78 @ 15%
and
27000 - x = $15,222.22 @ 9%.


Distributive-associative-commutative-properties/258032: [9-2(5-4)]
1 solutions

Answer 189877 by drk(1908) About Me  on 2010-01-18 13:46:35 (Show Source):
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here is the question:
%289-2%285-4%29%29
step 1 - start from inner most ( )
5-4 = 1, so we get
%289-2%281%29%29
step 2 - multiply 2x1 to get
9-2
step 3 - subtract to get
7


Exponents-negative-and-fractional/258031: how do you write 17,990,000 in scientific notation
1 solutions

Answer 189876 by drk(1908) About Me  on 2010-01-18 13:44:35 (Show Source):
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Notice there is no decimal - it is invisible all the way to the right of the number.
We want a number of the form a*10^b, where 0 So,
step 1 - from the given number move the decimal 7 jumps left.
step 2 - since we started with a number bigger than 10, the exponent must be positive.
step 3 - the answer is then
1.799 x 10^7


Polynomials-and-rational-expressions/257813: what is:
(3x-3 / (2x-5)^2) / (2x^2+3x-5 / 4x^2-25)
1 solutions

Answer 189708 by drk(1908) About Me  on 2010-01-17 19:27:01 (Show Source):
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The original problem is given as:
%28%283x-3%29+%2F+%282x-5%29%5E2%29+%2F+%28%282x%5E2%2B3x-5%29+%2F+%284x%5E2-25%29%29
step 1 - multiply by the reciprocal gets us
%28%283x-3%29%2F%282x-5%29%5E2%29%2A+%28%284x%5E2-25%29%2F%282x%5E2%2B3x-5%29%29
step 2 - factor to get

step 3 - cancel to get
3%2F%282x-5%29


Rectangles/257815: The length of a rectangle is 2 ft more than four times the width. Express as an interger the maximum width of the rectangle when the perimeter is less than 34 ft ?
1 solutions

Answer 189707 by drk(1908) About Me  on 2010-01-17 19:21:44 (Show Source):
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Let length = L and width = W.
from the given information, we get
L = 4W + 2
P = 2L + 2W
34 > 2(4W+2) + 2W
34 > 10W + 4
30 > 10W
3 > W
The maximum width is 2.
If W = 2
L = 10
P = 24 < 34
--
If W = 3
L = 14
P = 34 this is NOT LESS than 34.


Miscellaneous_Word_Problems/257783: Ricardo wants to replace the wooden door on his flat. The wooden door will be shaped like a rectangular solid and will measure 76 2/3 inches long and 44 1/4 inches wide; and will be 1 3/8 inch thick. How many cubic inches of wood will be needed for the door? Give solution exactly as a mixed number.

1 solutions

Answer 189704 by drk(1908) About Me  on 2010-01-17 19:17:30 (Show Source):
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I would suggest turning all fractions into improper then multiply.
76 and 2/3 = 230/3
44 and 1/4 = 177/4
1 and 3/8 = 11/8
--
%28230%2F3%29%2A%28177%2F4%29%2A%2811%2F8%29
reduced becomes
74635%2F16
which is
4664 + 11/16 cubic inches


Equations/257811: I'm trying to figure out the answer for 3m+4=19-2n

I tried 3m+4-4=19-2n-4
3m=15-2n
?


I get confused on these, thanks for your help
1 solutions

Answer 189703 by drk(1908) About Me  on 2010-01-17 19:05:28 (Show Source):
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Here is the original question
(i) 3m%2B4=19-2n
I notice you have two variables here. ALso M is next to the n on the keyboard, so it could be one variable. We have four options. Hopefully one of these will answer your question.
--
option 1 - solve (i) for m
3m%2B4=19-2n
subtract 4 from both sides to get
3m+=+19+-+4+-2n
divide by 3 to get
m+=+%28-2%2F3%29n+%2B+5
--
option 2 - solve (i) for n
3m%2B4=19-2n
subtract 19 from both sides to get
3m+%2B+4+-+19+=+-2n
divide by -2 to get
n+=+%28-3%2F2%29n+-+15%2F2
--
option 3 - m=n solve (i) for m
3m%2B4=19-2m
subtract 4 from both sides to get
3m+=+19+-+4+-2m
add 2m to both sides to get
5m+=+15
divide by 5 to get
m+=+3
--
option 4 - m=n solve (i) for n
3n%2B4=19-2n
subtract 4 from both sides to get
3n+=+19+-+4+-2n
add 2n to both sides to get
5n+=+15
divide by 5 to get
n+=+3


Mixture_Word_Problems/257812: A mixture of acid and water is 35% acid. if the mixture contains a total of 40 Liters, how many liters of pure acid are in the mixture? How many liters of pure water are in the mixture?
1 solutions

Answer 189700 by drk(1908) About Me  on 2010-01-17 18:58:01 (Show Source):
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This is a mixture problem. Be careful here, as pure acid = 100% acid and water = 0% acid. As a matter of fact any time they give you water it is automatically 0 in the % column. WE have the following table based on given information:
liquid . . . . . . . . . .% . . . . . . . . . . .L . . . . . . . . .%xL
acid . . . . . .. . . . . 100 . . . . . . . . . x . . . . . . . . .100x
water . . . . .. . . . . 0 . . . . . . . . . .. 40-x . . . .. . . . 0
mix . . . . .. . . . . . 35 . . . . . . . . . .40 . . . . . .. .. . 1400
From the third column, we get
100x = 1400
x = 14.
So we have
14 Liters of pure acid
26 liters of pure water


Polynomials-and-rational-expressions/257790: Can you plase help pme factor 4a^2+12ab+9b^2-25c^2
1 solutions

Answer 189699 by drk(1908) About Me  on 2010-01-17 18:53:50 (Show Source):
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Here is the original problem:
(i) 4a%5E2%2B12ab%2B9b%5E2-25c%5E2
look carefully, we really have this
(ii) 4a%5E2%2B12ab%2B9b%5E2-25c%5E2
which is the difference of two squares.
Factoring (ii), we get
%282a%2B3b%29%5E2 - %285c%29%5E2
factoring as a difference of two squares, we get
%282a%2B3b-5c%29%282a%2B3b%2B5c%29


Matrices-and-determiminant/257807: Use the row echelon method to solve the system of three equations in three unknowns.
x - y + 2z = -2
5x + z = 0
x + 2y+z = 4
1 solutions

Answer 189697 by drk(1908) About Me  on 2010-01-17 18:48:38 (Show Source):
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We are given the following:
x - y + 2z = -2
5x + z = 0
x + 2y+z = 4
--
in row echelon form, we have:
1 . . . . . (-1) . . . . . . .2 . . . . . . .(-2)
5 . . . . . .0 . . . . . . . .1 . . . . . . .0
1 . . . . . . 2 . . . . . . . 1 . . . . . .. 4
We need to get a diagonal matrix so take row 2 - 5 row 1 -> row 2; row 3 - row 1 -> row 3
--
1 . . . . . (-1) . . . . . . .2 . . . . . . .(-2)
0 . . . .. . 5 . . . . . . . .(-9) . . .. . . 10
0 . . . .. . 3 . . . . . .. . . -1 . . . . . . . 6
(1/5) row 2 -> row 2
--
1 . . . . . (-1) . . . . . . .2 . . . . . . .(-2)
0 . . . . . . 1 . . . . . . . .(-9/5) . . 2
0 . . . . . . 1 . . . . . . . .3 . . . . . . . 6
row 1 + row 2 -> row 1; row 3 - row 2 -> row 3
--
1 . . . . . . 0. . . . . . . .(1/5) . . . . 0
0 . . . . . . 1 . . . . . . . .(-9/5) . . . 2
0 . . . . . . 0 . . . . . . . .(22/5) . . . .0
(5/24) row 3 -> row 3
--
1 . . . . . . 0. . . . . . . .(1/5) . . . . 0
0 . . . . . . 1 . . . . . . . .(-9/5) . . . 2
0 . . . . . . 0 . . . . . . . .1 . . . . . . . 0
So,
z = 0
y = 2
x = 0
{0, 2, 0}


Travel_Word_Problems/257809: The distance from Melbourne to London is 10,500 miles. If a jet averages 500 mph between the two cities, What is its travel time in hours?
1 solutions

Answer 189690 by drk(1908) About Me  on 2010-01-17 18:30:53 (Show Source):
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This is: rate x time = distance. The rate = 500 and the distance = 10,500. we can use this formula to find the time as:
rate+%2A+time+=+distance
500+%2A+T+=+10%2C500
T+=+21+hours


Triangles/257796: Find the area of the triangle ABC having vertices A(7,-4) B(3,1) C(-10,-8)
1 solutions

Answer 189687 by drk(1908) About Me  on 2010-01-17 18:29:12 (Show Source):
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If you graph these out, you may notice that there are no right angles. This means we can use one of three formulas:
(1) Hero's formula - approximate
To use this we need the 3 distances. They are: sqrt(255), sqrt(61), sqrt(261)
The semi perimeter, s, is about 12.79
A = sqrt(s*(s-a)(s-b)(s-c))
A = 50.5
(2) matrices
Lets use matricies. If we apply matrices, we get 50.5
--
(3) 1/2absinC
This requires trig calculations, which I don't know you have seen.
--
So the area is 50.5.


Inverses/257805: Inverse of y=4x-2
y=2x+4
y=1/4x + 1/2
y= 1/4x-1/2
y=4x +1/2
1 solutions

Answer 189675 by drk(1908) About Me  on 2010-01-17 18:10:36 (Show Source):
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We stat with
y=4x-2+
step 1 - reverse the x and y to get
x+=+4y-2
step 2 - solve for the new y to get
x%2B2+=+4y
%28x%2B2%29%2F4+=+y%5E%28-1%29
separating our common denominator, we get
%281%2F4%29x%2B1%2F2+=+y%5E%28-1%29
So, the answer is y= 1/4x-1/2


Linear-equations/257804: find the slope x+2y=4
1 solutions

Answer 189674 by drk(1908) About Me  on 2010-01-17 18:07:51 (Show Source):
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Solving for y, we can get the slope
x%2B2y=4
subtract x to get
2y=-x%2B4
divide by 2 to get
y+=+%28-1%2F2%29x+%2B+2
The slope intercept form is
y+=+mx+%2B+b
matching these two equations, we see that
slope = m = (-1/2)


Matrices-and-determiminant/257803: A company makes 3 types of cable. Cable A requires 3 black wires, 3 white wires, and 2 red wires. Cable B requires 1 black, 2 white, and 1 red. Cable C requires 2 black, 1 white, and 2 red. If 95 black wires, 100 white wires, and 80 red wires were used, then how many of each cable were made?
1 solutions

Answer 189673 by drk(1908) About Me  on 2010-01-17 18:05:29 (Show Source):
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Here we have a 3x3 system.
Let the cables be A, B, and C.
(i) 3A + 1B + 2C = 95
(ii) 3A + 2B + 1C = 100
(iii) 2A + 1B + 2C = 80
--
Lets eliminate the B's. Take (ii) - 2*(i) to get
(iv) -3A -3C = -90
lets eliminate the B's. take (ii) - 2*(iii) to get
(v) -1A -3C = -60
--
To eliminate C's, take (v) - (iv) to get
(vi) 2A = 30 so
A = 15 cables
C = 15 cables
B = 20 cables


Graphs/257802: find the intercerpts and then use them to graph the equation 3y - 9 = 3x
1 solutions

Answer 189672 by drk(1908) About Me  on 2010-01-17 17:59:02 (Show Source):
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The x-intercept is when we let y = 0, and solve for x. We get
(i) 3%2A0+-+9+=+3x
x = -3
The y-intercept is when we let x = 0, and solve for y. We get:
(ii) 3y+-+9+=+3%2A0
y = 3
Now, we can graph these and create a line.
+graph%28+300%2C+200%2C+-10%2C+10%2C+-10%2C+10%2C+x%2B3%29+


Money_Word_Problems/257799: You want to have a $90,000 college fund in 11 years. How much will you have to deposit now under the scenario below. Assume that you make no deposits into the account after the initial deposit.
An APR of 5% compounded daily.
1 solutions

Answer 189671 by drk(1908) About Me  on 2010-01-17 17:56:24 (Show Source):
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We need the formula:
(i) A+=+P%281+%2B+%28r%2Fn%29%29%5E%28nt%29
from the given information, we have
(ii) 90000+=+P%281%2B%28.05%2F365%29%29%5E%28365%2A11%29
so,
(iii) 90000+=+P%281.73318773%29
dividing, we get
(iv) P+=+51927.44


Angles/257798: what angle is 5x's as large as its own complement
1 solutions

Answer 189670 by drk(1908) About Me  on 2010-01-17 17:52:45 (Show Source):
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Let x be an angle.
Complementary angles add to 90. So,
x = 5(90-x)
x = 450 - 5x
6x = 450
x = 75


Angles/257800: what angle is 10 degrees more than three times its own complement
1 solutions

Answer 189668 by drk(1908) About Me  on 2010-01-17 17:50:56 (Show Source):
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Let x be an angle.
Complimentary angles add to 90 degrees, so
x = 3(90-x)+10
x = 270 - 3x + 10
4x = 280
x = 70.


Graphs/257801: What is the slope of y= -10x +6
1 solutions

Answer 189667 by drk(1908) About Me  on 2010-01-17 17:49:18 (Show Source):
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The formula for slope is
y+=+mx+%2B+b
we are given
y+=+-10x+%2B+6
matching the equations up, we get
slope = m = -10.


Distributive-associative-commutative-properties/257788: solve for x
x(2x-1)=2x²+5x-12
1 solutions

Answer 189666 by drk(1908) About Me  on 2010-01-17 17:48:03 (Show Source):
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step 1 - distributive property on the left to get
(i) 2x%5E2+-+x+=++2x%5E2+%2B+5x+-+12
step 2 - simplify to get
(ii) 0+=+6x+-+12
step 3 - solve for x to get
(iii) x+=+2
checking, we get
2(2*2-1) = 2*2^2+5*2-12
2(3) = 16+10-12
6 = 6
+graph%28+300%2C+200%2C+-10%2C+10%2C+-10%2C+10%2C+2x%5E2-x%2C2x%5E2%2B5x-12%29+


Distributive-associative-commutative-properties/257789: Solve for x
4x(x+1)=(2x-3)(2x+5)
1 solutions

Answer 189663 by drk(1908) About Me  on 2010-01-17 17:33:15 (Show Source):
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step 1 - distributive property on the left and foil on the right to get
(i) 4x%28x%2B1%29=%282x-3%29%282x%2B5%29
(ii) 4x%5E2+%2B+4x+=+4x%5E2+%2B10x+-+6x+-+15
simplifies to
(iii) 0+=+-15
This is no solution
+graph%28+300%2C+200%2C+-10%2C+10%2C+-10%2C+10%2C+4x%5E2%2B4x%29+
+graph%28+300%2C+200%2C+-10%2C+10%2C+-10%2C+10%2C+4x%5E2%2B4x-15%29+


Trigonometry-basics/257759: How to solve this problem and the steps w/five key points?
y = Sin 4x? I'm a beginner can u help?
1 solutions

Answer 189653 by drk(1908) About Me  on 2010-01-17 17:00:22 (Show Source):
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This you really can't solve. You can simplify or graph.
(i) y+=+sin%284x%29
--
Now 4x = 2x + 2x, so we get
(ii) y+=+sin%282x+%2B+2x%29
we have an identity:
sin(A+B) = sinA cosB + sinB cosA
or in our case
(iii) Sin%282x%2B2x%29+=+sin2xcos2x+%2B+cos2xsin2x
But these are the same, so we can write
(Iv) 2sin%282x%29
--
Now 2x = x + x, so we get
(v) y+=+sin%28x+%2B+x%29
we have an identity:
sin(A+B) = sinA cosB + sinB cosA
or in our case
(vi) Sin%28x%2Bx%29+=+sinxcosx+%2B+cosxsinx
But these are the same, so we can write
(vii) 2sin%28x%29
From (iv) and (vii), we get
y+=+4sin%28x%29


Polynomials-and-rational-expressions/257734: (x-1)(x^2+10x+24=0...This one has me baffled..I can work 2nd set of parentheses but the (x-1) has got me confused.Is this a valid solvable problem?
1 solutions

Answer 189646 by drk(1908) About Me  on 2010-01-17 16:53:22 (Show Source):
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Here is the original question:
%28x-1%29%28x%5E2%2B10x%2B24%29=0
step 1 - factor the second polynomial to get
%28x-1%29%28x%2B6%29%28x%2B4%29=0
step 2 - set each pat = 0 and solve:
x-1 = 0
x = 1
x + 4 = 0
x = -4
x + 6 = 0
x = -6
we have three answers
{-6, -4, 1}


Graphs/257736: Lorena borrowed $100 from her father and plans to pay him back at a rate of $10 per week. The graph shows the amount Lorena owes her father. Find the equation that represents this relationship.
A. y= 10x - 100
B. y= 10x - 90
C. y= 100 - 10x
D. y= -100 - 10x
1 solutions

Answer 189600 by drk(1908) About Me  on 2010-01-17 15:10:44 (Show Source):
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The answer is [C]. We owe 100 and eventually pay the loan down to zero.


Graphs/257733: in direct variation if y varies directly with x:
find the equation for the direct variation if y=20 when x= 3 find x when y=8
1 solutions

Answer 189598 by drk(1908) About Me  on 2010-01-17 15:09:38 (Show Source):
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Step 1 write y = kx and find k using known x and y information.
y = kx
20 = 3k
k = 20/3
step 2 - rewrite the equation with your new K value as
y = (20/3)x
step 3 find x when y = 8
8 = (20/3)x
24/20 = x
x = 6/5


Word_Problems_With_Coins/257726: How many ways can you make $0.25 using pennies, nickels, dimes, and quarters

1 solutions

Answer 189597 by drk(1908) About Me  on 2010-01-17 15:07:39 (Show Source):
You can put this solution on YOUR website!
There appear to be 13 ways. Here they are in {p,n,d,q} form:
{p,n,d,q}
{0,0,0,1}
(0,1,2,0}
{5,0,2,0}
{0,3,1,0}
{5,2,1,0}
{10,1,1,0}
{15,0,1,0}
{0,5,0,0}
{5,4,0,0}
{10,3,0,0}
{15,2,0,0}
{20,1,0,0}
{25,0,0,0}