Multiple choice

A can do a work in 20 days. B can do it in 30 days. A starts the work but after 10 days he left. In how many days B can finish the remaining work?

  1. 30

  2. 10

  3. 20

  4. 15
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

A's 1 day work = 1/20, B's 1 day work = 1/30. A works for 10 days, completing 10/20 = 1/2 of the work. Remaining work = 1 - 1/2 = 1/2. B completes 1/2 work in (1/2) ÷ (1/30) = 15 days. Alternatively: total work = LCM(20,30) = 60 units. A does 3 units/day, B does 2 units/day. A completes 30 units in 10 days, leaving 30 units. B needs 30÷2 = 15 days.

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