Question

A rectangle is twice as long as it is wide. if its length is increase by 4 cm and its width is decreased by 3 cm, the new rectangle formed has an area of 100 cm2 . find the dimensions of the original rectangle.

Answer 1

Now the width is w.
It's twice as long as wide, so now the length is 2w.

If the length is increased by 4 cm, the length will be 2w + 4.
The width is decreased by 3 cm, so the width will be w - 3.

The are of the new rectangle is 100 cm^2.

area = length * width

area = (2w + 4)(w - 3)

The area of the new rectangle is 100, so we get

(2w + 4)((w - 3) = 100

2w^2 - 6w + 4w - 12 = 100

2w^2 - 2w - 112 = 0

w^2 - w - 56 = 0

(w - 8)(w + 7) = 0

w - 8 = 0   or   w + 7 = 0

w = 8   or   w = -7

A width cannot be negative, so discard w = -7.

w = 8

The width is 8 cm.
The length is twice the width, so the length is 16 cm.