Multiple choice

L and M together can complete a piece of work in 72 days, M and N together can complete it in 120 days, and L and N together in 90 days. In what time can L alone complete the work?

  1. 150 days

  2. 80 days

  3. 100 days

  4. 120 days
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

1/L + 1/M = 1/72, 1/M + 1/N = 1/120, 1/L + 1/N = 1/90. Sum = 2(1/L + 1/M + 1/N) = 1/72 + 1/120 + 1/90 = (5+3+4)/360 = 12/360 = 1/30. 1/L + 1/M + 1/N = 1/60. 1/L = 1/60 - 1/120 = 1/120. L = 120 days.

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