Test Index

WAEC Mathematics 2011 Paper

Question : 24

Total: 47

G varies directly as the square of H, If G is 4 when H is 3, find H when G = 100

Solution:

Concept:

Direct variation with a square means

G = kH^2

, where

k

is the constant of proportionality.

Explanation:

Since

G \propto H^2

, write

G = kH^2

Given

G = 4

when

H = 3

, substitute into the equation:

4 = k(3)^2

4 = 9k

k = \frac{4}{9}

Now substitute

G = 100

and

k = \frac{4}{9}

into

G = kH^2

100 = \frac{4}{9}H^2

Multiply both sides by

9

900 = 4H^2

Divide both sides by

4

H^2 = 225

Take the positive square root:

H = \sqrt{225} = 15

Answer:

H = 15

, so the correct option is A.

Go to Question:

Prev Question

Next Question