Multiple choice general knowledge math & puzzles

If it takes Bill 20 hours to paint a house and it takes George 30 hours, how long will it take if they work together yet independently?

  1. 11

  2. 13

  3. 12.5

  4. 12

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

Bill paints 1/20 house per hour, George paints 1/30 per hour. Together they paint 1/20 + 1/30 = 5/60 = 1/12 house per hour. So time needed = 12 hours. Add rates, then take the reciprocal.