If y varies directly as x, and y=9 when x=4, how do you find y when x=16?

1 Answer
Jan 13, 2017

When x=16, y=36.

Explanation:

If y varies directly as x, then if y increases, x increases, and if y decreases, x decreases. We can express this idea very succinctly in mathematics by writing y = kx. Where k is a constant. Using this equation and substituting the initial values we have:
y = kx
9 = k*4
So k= 9/4
Hence we can rewrite our general relationship more particularly in this case as y = 9/4 x.
Using the second set of values and our specific equation we get:
y = 9/4 *16
So y = 36