Question

The value of y varies directly with x, and y = 12 when x = 8.

Find y when x = 15.

Answer 1

Okay so direct variation means that we can write the relation on the form
\[ y = kx \]
You said x=8 when y=12 that means that
\[ 12 = k*8 \\
k = \frac{12}{8} = \frac{3}{2} \]
So our relation is just
\[ y = \frac{3}{2}x \]
Putting in x=15 gives
\[ y = \frac{3}{2}*15 = 22.5 \]

Answer 2

22.5