Multiple choice general knowledge math & puzzles

A can complete a job in 20 days. B can do it in 30 days. A and B start working together and A leaves 10 days before the job is done. In how many days will the job be completed?

  1. 18

  2. 27

  3. 26.67

  4. 16

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

Let total days = d. A works for (d-10) days at rate 1/20 per day. B works for d days at rate 1/30 per day. Equation: (d-10)/20 + d/30 = 1. Solving: (3(d-10) + 2d)/60 = 1 → 5d-30 = 60 → 5d = 90 → d = 18. Check: A works 8 days (8/20 = 0.4), B works 18 days (18/30 = 0.6), total = 1 job.