Multiple choice

Annie can do a piece of work in 9 days. Bob can do the same work in twice that time. Mack can only do 3 4 as much work as Annie does in one day. How long will Annie, Bob and Mack, working together, take to do the same job?

  1. 5 days

  2. 6 days

  3. 4 days

  4. 12 days

  5. 10 days
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Annie rate = 1/9. Bob rate = 1/18. Mack rate = 3/4 * (1/9) = 1/12. Combined rate = 1/9 + 1/18 + 1/12 = (4+2+3)/36 = 9/36 = 1/4. Time = 4 days.

AI explanation

Let the total work be the least common multiple of the given days, which is 36 units. Annie completes 4 units per day, Bob completes 2 units per day since he takes twice the time, and Mack completes 3 units per day as he does 3/4 of Annie's daily work. Working together, their combined daily work is 4 + 2 + 3 = 9 units, so they will complete the 36 units of work in 36 divided by 9, which is 4 days.

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