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Recent problems solved by 'oberobic'
oberobic answered: 2303 problems
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(Do not convert the percentages below ( whay exactly does this mean and if I do not convert the percents to decimal form how can I find the answer?)
What is the cost to remove 15% of the pollutant?
What is the cost to remove 25% of the pollutant?
What is the cost to remove 45% of the pollutant?
What is the cost to remove 65% of the pollutant?
What is the cost to remove 85% of the pollutant?
1 solutions
Answer 351502 by oberobic(2304)   on 2011-11-19 21:59:37 (Show Source):
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Permutations/534398: A typical Social Security number is 555-47-5593. How many Social Security numbers are possible if the first two digits cannot be 0?
1 solutions
Answer 351501 by oberobic(2304) on 2011-11-19 21:58:15 (Show Source):
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Quadratic_Equations/534401: Find the vertex the line of symmetry, the maximum or minimum value of the f(x). Graph the function.
f(x)= -(x+3)^2-9
1 solutions
Answer 351499 by oberobic(2304) on 2011-11-19 21:43:13 (Show Source):
You can put this solution on YOUR website!f(x) = -(x+3)^2 -9
f(x) = -(x^2 +6x +9) -9
f(x) = -x^2 -6x -9 -9
f(x) = -x^2 -6x -18
.
axis of symmetry
-b/2a = -(-6)/(2*(-1)) = 6/-2 = -3
.
vertex is on the axis of symmetry
-(-3)^2 -6(-3) -18 = -9+18-18 = -9
(-3,-9)
.
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Polygons/534410: a regular polygon has an interior angle with a measurement of 160 degrees. How many sides does the polygon have?
1 solutions
Answer 351496 by oberobic(2304) on 2011-11-19 21:36:40 (Show Source):
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Travel_Word_Problems/534407: A car traveling 88 km/hr is 110 m behind a truck traveling 75 km/hr. How long will it take the car to reach the truck?
1 solutions
Answer 351495 by oberobic(2304) on 2011-11-19 21:28:24 (Show Source):
You can put this solution on YOUR website!I assume the car is 110 km behind the truck.
The difference in their speeds is 88-75 = 13 km/hr.
The car needs to make up 110 km.
t = d/r
t = 110/13
t = 8.46 hr for the car to catch up
8.46 hr = about 8 hr 28 min
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Linear-equations/534395: The directions say : Write the equation of the line that contains the points. Express final equation in standard form.
(-2,-3),(2,7)
I already have m=5/2. I dont know how to write the equation.
1 solutions
Answer 351492 by oberobic(2304) on 2011-11-19 21:21:32 (Show Source):
You can put this solution on YOUR website!y = mx + b
.
m = (-3-7)/(-2-2)
m = -10/-4
m = 5/2
.
y = 5/2x + b
.
Use the point (2,7) to find 'b'.
.
7 = 5/2*2 + b
7 = 5 + b
b = 2
.
y = 5/2x + 2
.
y-intercept = (0,2)
.
x-intercept = (-4/5,0)
.
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Travel_Word_Problems/534406: two locomotives approach each other on parallel tracks. Each has a speed of 95 km/h with respect to the ground. If they are initially 8.5 km apart, how long will it be before they reach each other?
1 solutions
Answer 351489 by oberobic(2304) on 2011-11-19 21:15:54 (Show Source):
You can put this solution on YOUR website!The two locomotives are closing on one another at the sum of their speeds: 95+95 = 190 km/hr.
The start at 8.5 km apart, so they will meet each other pretty soon.
t = 8.5 km/ 190 km/hr
t = 0.0447368421 hr
.
That is a precise but not terribly useful answer.
.
0.0447368421 hr * 60 min/hr = 2.68 minutes
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Graphs/534393: find the x-intercept and y-intercept
f(x)= -x^2+2x+63
I need the x coordinates of the intercepts
and
the y intercepts (0, )
1 solutions
Answer 351485 by oberobic(2304) on 2011-11-19 21:03:29 (Show Source):
You can put this solution on YOUR website!factor
.
-x^2 +2x +63 = 0
.
(-x -7)(x -9)
.
Check using FOIL.
.
-x^2 +9x -7x +63 = -x^2 +2x +63
.
Roots
.
x = -7 or 9
.
.
By inspection, you can see the y-intercept is (0,63).
You also can find it by setting x=0 and solving the equation.
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Linear-equations/534331: what is the slope and y intercept of the following:
y=6x+11
y=1/4x-2/7
what is an equation of a line with the following given slope:
m=1,b=-4
1 solutions
Answer 351473 by oberobic(2304) on 2011-11-19 20:03:43 (Show Source):
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Probability-and-statistics/534367: 1.what is the expected number of days per month this year to two decimal places?
2.what if you exclude the months that end in " from the previous question?
1 solutions
Answer 351470 by oberobic(2304) on 2011-11-19 20:00:19 (Show Source):
You can put this solution on YOUR website!The expected number of days per month = sum of days per month / 12 months.
In 2011, there are 365 days.
365/12 = 30.42 days per month
.
If you exclude months that end in "R" that means you exclude 4 months: September, October, November, and December. They total 30+31+30+31 = 122 days.
.
365 - 122 = 243 days
.
243/8 = 30.38
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Mixture_Word_Problems/534337: pure acid is to be added to a 10% acid solution to obtain 42 L of a 40% acid solution. What amounts of each should be used?
blank L of pure acid solution and blank L of 10% acid solution
1 solutions
Answer 351461 by oberobic(2304) on 2011-11-19 18:46:46 (Show Source):
You can put this solution on YOUR website!x = amount 10% acid
y = amount of pure acid
.
x+y = 42 liters
x = 42-y
y = 42-x
.
The desired solution is 42 liters of a 40% solution. It will contain 42*.40 liters of pure acid.
42*.4 = 16.8 liters of pure acid and 25.2 liters of solvent (probably water).
.
10%*x + 100%*y = 40%*42
.1*x + y = 16.8
.
multiply both sides by 10 to eliminate the decimals
.
x + 10y = 168
.
substitute for x = 42-y
.
42-y +10y = 168
9y = 126
y = 126/9 = 42/3 = 14
.
x = 42-14
x = 28
.
Check how much 'pure' acid is in the solution.
28 * 10% acid = 2.8 liters of pure acid
13 * 100% acid = 14 liters of pure acid
2.8 + 14 = 16.8 liters of pure acid in the 42 liters of solution
.
Answer: Mix 14 liters of pure acid and 28 liters 10% acid to make 42 liters of 40% acid.
.
Done.
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Graphs/534274: write the slope-intercept form of the equation of the line that is perpendicular to 2x-5y=10 and passes through points (2,4)
1 solutions
Answer 351443 by oberobic(2304) on 2011-11-19 16:24:43 (Show Source):
You can put this solution on YOUR website!The slope intercept form of a linear equation is: y=mx+b.
.
2x -5y = 10
-5y = -2x +10
y = 2/5*x -2
.
The line perpendicular to this line will have a slope = inverse reciprocal: -5/2.
.
y = -5/2*x + b
.
Use the point (2,4) to find 'b'.
.
4 = -5/2*2 + b
4 + 5 = b
b = 9
.
y = -5/2*x + 9
.
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test/534284: Roger bought hamburgers at a cost of $9 per dozen and bagels at a cost of $3 per dozen. He bought a total of 45 dozens and paid a total of $225. How many dozens of hamburgers and how many dozens of bagels did he buy?
1 solutions
Answer 351435 by oberobic(2304) on 2011-11-19 15:21:44 (Show Source):
You can put this solution on YOUR website!h = number of dozens of hamburgers
9h = cost of the hamburgers
b = number of dozens of bagels
3b = cost of the bagels
.
h + b = 45
so
h = 45-b
and
b = 45-h
.
9h + 3b = 225
.
Multiply the first equation by 3.
.
3h + 3b = 135
9h + 3b = 225
--------------
-6h = -90
.
h = -90/-6
h = 15
.
b = 45-15
b = 30
.
Answer: 15 dozen hamburgers and 30 dozen bagels.
.
Check the cost.
15*9 + 30*3 = 225
Correct.
.
Done.
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Geometry_Word_Problems/534275: The perimeter of a triangle with 2 equal sides is 71 cm. if its base were lengthened by 6cm and each leg were shortened by 4cm, all 3 sides would be equal. Find the length of the base of the original triangle
1 solutions
Answer 351433 by oberobic(2304) on 2011-11-19 15:16:22 (Show Source):
You can put this solution on YOUR website!2s + b = 71
b = 71-2s
.
s-4 = b+6
b = s-4-6
b = s-10
.
b=b
so
71-2s = s-10
71+10 = s+2s
3s = 81
s = 27
.
2s + b = 71
2*27 + b = 71
b = 71 -54
b = 17
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Answer: The original triangle has sides = 27 and base = 17.
.
Check.
b+6 = 17+6 = 23
s-4 = 27-4 = 23
So that would make all sides equal.
.
Done.
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Polynomials-and-rational-expressions/534249: a partial solution set is given for each equation. Find complete solution set:
x^3 + 3x^2 - 13x -15 =0 {-1}
i keep getting 1 -2 -13 and -4 as the ansers for each when i subract. What am i doing wrong??
the answer is {-1,-5,3} and im not even close
1 solutions
Answer 351427 by oberobic(2304) on 2011-11-19 14:47:31 (Show Source):
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Numbers_Word_Problems/534261: One number is 7 less than a second number. Twice the second number is 4 less than 5 times the first. Find the smaller of two numbers.
1 solutions
Answer 351424 by oberobic(2304) on 2011-11-19 14:40:05 (Show Source):
You can put this solution on YOUR website!Define the two numbers as
x
x+7
.
2(x+7) + 4 = 5x
2x + 14 +4 = 5x
18 = 3x
3x = 18
x = 6
.
x+7 = 13
.
One number is 7 less than another.
6 is 7 less than 13.
Correct.
.
Twice the second number = 2*13 = 26
Is 26 4 less than 5 times the first number.
5*6 = 30
30-26 = 4
Correct.
.
Re-read the question to determine what the answer needs to be.
.
Answer: The smaller of the two numbers is 6.
.
Done.
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Linear-systems/534228: solve system of equations by graphing. Then classify the system
2x-6y=54
3x-9y=-18
1 solutions
Answer 351422 by oberobic(2304) on 2011-11-19 14:29:00 (Show Source):
You can put this solution on YOUR website!2x -6y = 54
-6y = -2x + 54
y = (-2x)/-6 + 54/-6
y = 1/3*x - 9
.
3x - 9y = -18
-9y = -3x -18
y = (-3x)/-9 -18/-9
y = 1/3x + 2
.
With the same slope, the lines will be parallel.
.
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