Multiple choice

C is 5 times as efficient as B. A takes 60 days to complete a task. If A, B and C working together can complete the task in 12 days. In how many days can B complete the task if he worked alone?

  1. 80

  2. 75

  3. 90

  4. 95
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

C is 5 times as efficient as B, so C's work rate is 5 times B's rate. If B alone takes x days, B's rate is 1/x and C's rate is 5/x. A takes 60 days (rate 1/60). Together: 1/60 + 1/x + 5/x = 1/12. Solving: 1/60 + 6/x = 1/12, so 6/x = 1/12 - 1/60 = 4/60 = 1/15, giving x = 90.

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