Multiple choice

A, B and C can together do a job in 9 days. C alone can do the job in 36 days. In how many days can A and B do 50% of the job working together?

  1. 6

  2. 12

  3. 9

  4. 15
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A+B+C = 1/9 per day. C = 1/36 per day. Therefore, A+B = 1/9 - 1/36 = 4/36 - 1/36 = 3/36 = 1/12 per day. To complete 50% of the job (1/2), they need (1/2) / (1/12) = 6 days.

AI explanation

A and B's combined rate is 1/9 of the job per day, and C's rate is 1/36 per day. Subtracting C's rate from the total rate gives (1/9) - (1/36) = 3/36 = 1/12, meaning A and B together complete the job in 12 days. To find the time for 50% of the job, you multiply 12 days by 0.5 to arrive at 6 days.

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