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

Answer:

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#