Multiple choice

$A$ can complete a work in 9 days, $B$ in 10 days and $C$ in 15 days. $B$ and $C$ together started the work but left the work after 2 days. The time taken to complete the remaining work by $A$ will be

  1. $6$ days
  2. $8$ days
  3. $9$ days
  4. $5$ days
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

B and C together complete 1/10 + 1/15 = 1/6 of the work per day. In 2 days, they complete 1/3 of the work, leaving 2/3 of the work remaining. A, who completes 1/9 of the work per day, will take (2/3) / (1/9) = 6 days to finish the remaining work.

AI explanation

The combined one-day work of B and C is one-tenth plus one-fifteenth, which equals one-sixth, so in 2 days they complete one-third of the work. The remaining work is 1 minus one-third, which is two-thirds. A completes the work alone at a rate of one-ninth per day, so the time taken is two-thirds divided by one-ninth, resulting in 6 days.

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