Multiple choice

A can complete a certain work in 30 days. A started the work and B joined him after 4 days and the work was completed in total 20 days. In how many days can B alone complete the work?

  1. 42

  2. 45

  3. 48

  4. 50

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

A's work rate is 1/30 per day. In 4 days, A completes 4/30 work, leaving 26/30. A and B together complete the remaining 26/30 in 16 days, so (1/30 + 1/B) × 16 = 26/30. This gives 1/B = (26/30 - 16/30) / 16 = 10/480 = 1/48. Therefore B alone takes 48 days.

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