Question

If y varies directly with x and y = -18 when x = 18, find x when y = -5.

Write and solve a direct variation equation to find the answer.

Answer 1

x = 5

Explanation:

given y varies directly with x then the equation relating them is

y = kx ← k is the constant of variation

to find k use the condition y = - 18 when x = 18 , then

- 18 = 18k ( divide both sides by 18 )

- 1 = k

y = - x ← equation of variation

when y = - 5 , then

- 5 = - x ( multiply both sides by - 1 )

5 = x