X varies directly as y. If x is 9 when y is 4, find x when y is 8.

a) Write the variation.

b) Find x when y is 8.

Step-by-step explanation:

X ∝ y

introducing proportionality constant, we have

x = ky

given : x = 9 when y = 4, substitute the given values into the equation in order to get the constant

i. e 9 = k x 4

k = 9/4

substitute k = 9/4 into the equation in order to get the formula connecting x and y

⇒ x = 9/4 y

(b) To find x when y = 8, substitute the value of y into the formula

i. i x = 9/4 x 8

x = 9 x 2

x = 18