Multiple choice

A work can be finished by A in 12 days and by B in 15 days. If they work together, the number of days required to complete the work is

  1. 6

  2. 6 2/3

  3. 7 3/4

  4. 14
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A's rate is 1/12, B's rate is 1/15. Combined rate = 1/12 + 1/15 = (5+4)/60 = 9/60 = 3/20. Time taken = 20/3 = 6 2/3 days.

AI explanation

Using the combined work formula, A's rate is 1/12 and B's rate is 1/15. Their combined rate is (1/12) + (1/15) = (5 + 4) / 60 = 9/60 = 3/20 of the work per day. Inverting this fraction gives the total time required, which is 20/3 or 6 2/3 days.

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