Multiple choice

If X and Y work on a job for 8 days, which X alone can do in 30 days and Y alone can do in 40 days, then the fraction of work left is

  1. 4/5

  2. 8/15

  3. 1/5

  4. cannot be determined
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

X's rate = 1/30, Y's rate = 1/40. Combined rate = 1/30 + 1/40 = 7/120. Work done in 8 days = 8 * (7/120) = 7/15. Work left = 1 - 7/15 = 8/15.

AI explanation

Let the total work be 120 units, which is the least common multiple of 30 and 40. The daily work capacity of X is 4 units and Y is 3 units. Working together, their combined daily capacity is 7 units. In 8 days they complete 56 units, leaving 64 units unfinished. The fraction of work left is 64 divided by 120, which simplifies to 8/15.

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