Question

If y varies directly as x and y = 15 when x=-5, find y when x= 7.

A. -21
B. 21
C. 105
D. -35​

Answer 1

A. -21

Explanation:

y varies directly as x

y = kx

----------------------

y = 15 when x = -5

Find k, the constant of variation

15 = k(-5)

Divide both sides by -5

-3 = k

k = -3

------------------------------

y when x= 7

using k = -3

y = -3(7)

y = -21