Multiple choice

A can do a piece of work in 4 days. B can do it in 5 days. With the assistance of C they completed the work in 2 days. Find in how many days can C alone do it?

  1. 20 days

  2. 10 days

  3. 5 days

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

A's rate = 1/4, B's rate = 1/5. Combined rate (A+B+C) = 1/2. C's rate = 1/2 - (1/4 + 1/5) = 1/2 - 9/20 = 1/20. C takes 20 days.

AI explanation

Using the LCM method, let the total work be the least common multiple of 4, 5, and 2, which is 20 units. A completes 5 units per day, B completes 4 units per day, and together they complete 10 units per day. The combined daily work of A and B is 9 units, meaning C contributes 1 unit per day to the total output of 10 units. Therefore, C alone would take 20 days to complete the 20 units of work.

Keep practicing — related questions