Jordana was shown this diagram of an isosceles trapezoid and its reduction. She was asked to find the perimeter of the reduced trapezoid. Her work is shown below.

Question

A trapezoid with side lengths 30 centimeters, 12 centimeters, and 36 centimeters. A trapezoid with side lengths A, 4 centimeters, B.
Figures not drawn to scale.

Jordana’s Work
Scale factor
StartFraction 4 over 12 EndFraction = one-third
Side A
30 times one-third = 10
Side B
30 times one-third = 10
Perimeter
10 + 10 + 4 + 4 = 28

Where, if any, did Jordana first make a mistake in her work?
Jordana made a mistake when finding the scale factor.
Jordana made a mistake when she calculated the length of side A.
Jordana made a mistake when she calculated the length of side B.
Jordana did not make any mistakes in her work.

Answer 1

Jordana made a mistake when she calculated the length of side B.

The correct calculation should be:
Side B = 12 * 1/3 = 4

Therefore, the perimeter of the reduced trapezoid should be:
10 + 10 + 4 + 4 = 28

So Jordana did make a mistake in her work.