An 80 pound child sits 4 feet from the centre of a seesaw. How far from the centre must a 64 pound child sit to balance it?

Correct answer to question 69 (Mechanical Comprehension): 5 feet

Method

Balance needs weight times distance to match on both sides. The first child gives 80 x 4 = 320, so the second needs 320 / 64 = 5 feet. The lighter child sits further out, which is the sensible check on the answer.