SOLUTION: 1/ If varies inversely as the square of X, and y=16 when x=5, find y when x=2. 2/ Johnny can paint a car 5 hours. If Johnny works with Larry they can paint the car in 3 hours. H

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Question 921602: 1/ If varies inversely as the square of X, and y=16 when x=5, find y when x=2.
2/ Johnny can paint a car 5 hours. If Johnny works with Larry they can paint the car in 3 hours. How long does it take Larry to paint the car by himself?

Found 2 solutions by stanbon, josgarithmetic:
Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
1/ If y varies inversely as the square of X, and y=16 when x=5, find y when x=2.
y = k/x^2
Solve for "k" using "y = 16 when x = 5"::
16 = k/5^2
k = 400
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Equation::
y = 400/x^2
Find y when x = 2
----
y = 400/2^2 = 100
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2/ Johnny can paint a car 5 hours. If Johnny works with Larry they can paint the car in 3 hours. How long does it take Larry to paint the car by himself?
Johnny's rate:: 1/5 job/hr
Together rate:: 1/3 job/hr
Larry's rate:: 1/x job/hr
----
Equation:
rate + rate = together rate
1/5 + 1/x = 1/3
------
3x + 15 = 5x
2x = 15
x = 7.5 hrs (time for Larry to do the job alone.
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Cheers,
Stan H.
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Answer by josgarithmetic(39625) About Me  (Show Source):
You can put this solution on YOUR website!
"1/", you want to say this:
"If y varies inversely as the square of x,..."

y=k%2Fx%5E2, and you want to use the first data point to solve the value of k.
k=y%2Ax%5E2
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k=16%2A5%5E2
k=16%2A25
k=400
-
highlight%28y=400%2Fx%5E2%29


"2/":
Their combined rate is the sum of their individual rates. Be sure you arrange the rates for the unit of JOBS per HOUR, or JOB per HOURS.