Question

Given that y varies directly as x when y = 8 and x=5.

(a) express y in terms of x, and hence
(b) find y when x=30

Answer 1

(a) y = 1.6x

(b) y = 48

Explanation:

(a) Since y varies directly as x,

y ∝ x

y = kx [where k = proportionality constant]

If y = 8 and x = 5

By substituting these values in the equation,

8 = 5k

k =
`(8)/(5)`

k = 1.6

Therefore, equation will be,

y = 1.6x

(b) If x = 30, then we have to find the value of y.

By substituting the value of x in the equation,

y = 1.6 × 30

y = 48