A firefighter’s ladder of length 13 m is kept at a distance of 5 m from a building to reach a window. At what height is the window from the ground?

Correct answer: 12 m. By the Pythagorean theorem, height = √(13² − 5²) = √144 = 12 m.

Background: The ladder is the hypotenuse of a right triangle.

• 10 m: 10 m does not satisfy 5² + h² = 13².
• 15 m: 15 m is longer than the ladder.
• 20 m: 20 m is longer than the ladder.

Did you know? 5-12-13 is a common Pythagorean triple.

Memory trick: 5-12-13 triangle.