Multiple choice

A, B and C can do a piece of work in 7 days, 14 days and 28 days respectively. How long will they taken, if all the three work together?

  1. 4 days

  2. 5 days

  3. 6 days

  4. 3 days
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A Correct answer
Explanation

Combined rate = 1/7 + 1/14 + 1/28 = (4+2+1)/28 = 7/28 = 1/4. Time = 1 / (1/4) = 4 days.

AI explanation

Using the LCM method, let the total work be the least common multiple of 7, 14, and 28, which is 28 units. A completes 4 units per day, B completes 2 units per day, and C completes 1 unit per day. Working together, their combined daily output is 4 plus 2 plus 1, which equals 7 units. Dividing the total 28 units of work by their combined daily rate of 7 units gives a result of 4 days.

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