If z varies directly as x, and z =30 when x=8, find z when x=4.

Question

how do you know what is K and what is Y in the formula y=kx k=y/x

Answer 1

Direct variation means that z = k(x)  use the first relation to solve for k

 

30 = 8k

 

k = 15/4

 

When x is 4

 

z = (15/4)4 = 15