hardNumbersAll teasers

When are clock hands at right angles?

How many times do the hour and minute hands form a right angle between noon and midnight? From the free puzzle set on Think Fanny — next try Odd one out: 3, 5, 7, 9, 11, 13.

Think Fanny math brain teaser equations on a blackboard

The puzzle

Between 12:00 and 24:00, how many times do the hour hand and the minute hand form a perfect right angle (90 degrees)?

Count carefully. The obvious answer is wrong.