Xvaries 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