Multiple choice

A does 4/5 of a work in 20 days. He then calls B and they together finish the remaining work in 3 days. How long B alone would take to do the whole work?

  1. 23 days

  2. 37 days

  3. 75/2 days

  4. 40 days
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

A does 4/5 in 20 days, so A's rate is 1/25 per day. Remaining work is 1/5. Together they do 1/5 in 3 days, so combined rate is 1/15. B's rate = 1/15 - 1/25 = (5-3)/75 = 2/75. B takes 75/2 days.

AI explanation

If A completes 4/5 of the work in 20 days, A's rate is calculated as (4/5) / 20, which equals 1/25 of the work per day. The remaining work is 1/5, which A and B complete in 3 days, meaning their combined rate is (1/5) / 3, equaling 1/15 of the work per day. Subtracting A's rate from their combined rate gives B's rate: 1/15 minus 1/25 equals 5/75 minus 3/75, which is 2/75 of the work per day. Therefore, B alone would take the reciprocal of 2/75, or 75/2 days, to complete the whole work.

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