Multiple choice

Working alone, A can do a piece of work in 72 days and B in 90 days. If they work on it together for 10 days, then what fraction of work will be left?

  1. 1/4

  2. 3/5

  3. 1/5

  4. 3/4
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

A's rate = 1/72, B's rate = 1/90. Combined rate = 1/72 + 1/90 = (5+4)/360 = 9/360 = 1/40. Work done in 10 days = 10 * (1/40) = 1/4. Work left = 1 - 1/4 = 3/4.

AI explanation

A's one-day work is 1/72 and B's one-day work is 1/90. Their combined one-day work is 1/72 + 1/90, which equals 9/360 or 1/40. In 10 days, they complete 10 multiplied by 1/40, which is 1/4 of the work. The fraction of work left is 1 minus 1/4, which equals 3/4.

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