Question 1197034: Given that M is directly proportional to P, and M = 15 when P = 75, find M when P = 25.
M =________?
Found 2 solutions by ewatrrr, greenestamps:
Answer by ewatrrr(24785)   (Show Source):
You can put this solution on YOUR website!
Hi
M varies directly as P
That is: M = kP
Given:
M = 15 when P = 75
15 = 75k, 
find M when P = 25.
M = kP
M =  = 5
Wish You the Best in your Studies.
Answer by greenestamps(13200)  (Show Source):
You can put this solution on YOUR website!
I will guess that all of these direct and inverse variation problems that received responses from tutor @ewatrrr were posted by the same student. So I will respond to this one post; but my response applies to all the other similar problems.
In her responses, the other tutor always takes the given direct or inverse proportion and the given information to solve for the constant of proportionality, k. If you were finding a formula based on given information which you were then going to use for multiple later calculations, then that is a good way to go.
But in a problem like this, where you only need to find one other number based on the given information, all that work to find the value of k is unnecessary. You only need to use the information about direct or inverse variation to solve the problem.
The quick and easy path to the answer to this particular problem is this:
The value of one of the variables changes from 75 to 25, a factor of 1/3; since the variation is direct, the value of the other variable changes by a factor of 1/3.
ANSWER: 15(1/3) = 5
Of course, if in another problem the variation was inverse and one of the variables changed by a factor of 1/3, the value of the other variable would change by a factor of 3.
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