Multiple choice general knowledge math & puzzles

A 20 foot pole casts a 5 foot shadow. If, at the same time of day, a building casts a shadow 20 feet, how high is the building?

  1. 400 feet

  2. 4 feet.

  3. 80 feet.

  4. 100 feet.

Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

This is a similar triangles problem. The pole and its shadow form a right triangle with ratio 20:5 = 4:1. The building and its shadow form a similar triangle, so the building's height is 4 times its shadow length. 4 × 20 = 80 feet. Option A (400) incorrectly multiplies 20 × 20, option B (4) uses the inverse ratio, and option D (100) has no clear mathematical basis.