SOLUTION: For the following problem, y varies directly as x. If y = 25 when x = -15, find x when y is 10.

Algebra ->  Equations -> SOLUTION: For the following problem, y varies directly as x. If y = 25 when x = -15, find x when y is 10.      Log On


   

Question 1056244: For the following problem, y varies directly as x.
If y = 25 when x = -15, find x when y is 10.
Answer by Edwin McCravy(20059) About Me  (Show Source):
You can put this solution on YOUR website!
y varies directly as x.
y%22%22=%22%22k%2Ax

If y = 25 when x = -15, 
Substitute that in

25%22%22=%22%22k%2A%28-15%29

Solve for k

Multiply both sides by -15

25%2F%28-15%29%22%22=%22%22k

-5%2F3%22%22=%22%22k

Substitute that in 

y%22%22=%22%22k%2Ax

y%22%22=%22%22expr%28-5%2F3%29x  <-- that's the formula

find x when y is 10.
Substitute 10 for y

y%22%22=%22%22expr%28-5%2F3%29x

10%22%22=%22%22expr%28-5%2F3%29x

Multiply both sides by 3

30%22%22=%22%22-5x

Divide both sides by -5

-6%22%22=%22%22x

Edwin