Multiple choice

A can do a certain work in 15 days. B is 25% more efficient than A. Both worked together for 4 days. C alone completed the remaining work in 8 days. A, B and C together will complete the same work in?

  1. 5 days

  2. 6 days

  3. 4 days

  4. 7 days
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A's work rate = 1/15 per day. B is 25% more efficient, so B's rate = 1.25 × 1/15 = 1/12 per day. In 4 days, A+B complete 4×(1/15+1/12) = 3/5 of work. Remaining 2/5 is done by C in 8 days, so C's rate = (2/5)/8 = 1/20 per day. Combined rate = 1/15+1/12+1/20 = 1/5, so time = 5 days.

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