Multiple choice

A and B can do a piece of work in 20 days and 30 days respectively. They started the work together but after 8 days they decide to work on alternate days, starting with B. In how many days the work will be completed?

  1. 20 days

  2. 16 days

  3. 15 days

  4. 12 days

  5. None of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A's 1-day work = 1/20, B's 1-day work = 1/30. Together in 8 days: 8 × (1/20 + 1/30) = 8 × 5/60 = 40/60. Remaining work = 20/60. On alternate days starting with B: B does 2/60, then A does 3/60, and so on. After 7 more days, total = 57/60. On day 16, A completes remaining 3/60. Total = 16 days.

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