# If the values of s and t are directly proportional and s =8 when t =10, what is the value of s when t = 15?

Jan 18, 2017

When $t = 15$, $s = 12$.

#### Explanation:

If $s$ and $t$ are directly proportional, then $t = c s$ for a real constant $c$.

$10 = 8 c \implies c = \frac{10}{8} = \frac{5}{4}$

This means when $t = 15$, $15 = \frac{5}{4} s \implies s = 15 \cdot \frac{4}{5} = \frac{60}{5} = 12$.

For this problem, we had to remember that $\frac{a}{\frac{b}{c}} = a \cdot \frac{c}{b}$.