Multiple choice

X and Y together can complete a work in 12 days. X alone can complete in 20 days. If Y does the work only half a day daily, then in how many days X and Y together will complete the work?

  1. 10 days

  2. 20 days

  3. 11 days

  4. 15 days

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

Combined rate: 1/12 work per day. X's rate: 1/20 per day. Y's full-day rate: 1/12 - 1/20 = 5/60 - 3/60 = 2/60 = 1/30. Y working half-day: rate = 1/60 per day. Combined with half-day Y: 1/20 + 1/60 = 3/60 + 1/60 = 4/60 = 1/15. So they complete in 15 days.