Question

If y varies directly as x and y = 21 when x = 5, find x when y = 42.

Answer 1

Answer: 10

Step-by-step explanation:

varies directly means: $\frac{y}{x} = k$

Step 1: solve for k   ⇒  $\frac{21}{5} = k$

Step 2: plug in the given value and k to solve for the missing value: $\frac{42}{x} = \frac{21}{5}$

42(5) = 21(x)

$\frac{42(5)}{21} = \frac{21(x)}{21}$

2(5) = x

10  = x