Question

Tinh has a triangle with side lengths 12 mm, 15 mm, and 18 mm. He wants to reduce the triangle by one-third, so he divides each side length and each angle measure by 3. Which describes Tinh’s reduction?
Tinh’s reduction is incorrect; he should have only divided the side lengths by 3.
Tinh’s reduction is incorrect; he should have only divided the angle measures by 3.
Tinh’s reduction is incorrect; he should have multiplied the side lengths by 3 instead.
Tinh’s reduction is incorrect; he should have multiplied the angle measures by 3 instead.

Answer 1

Tinh’s reduction is incorrect; he should have only divided the side lengths by 3.

Reason: a reduction by one-third is a similarity with linear scale factor 1/3, so all side lengths are divided by 3 but angle measures remain the same. (If you divided each angle by 3 their sum would be 60°, not 180°.)