A, B, C alone can do a piece of work in 9, 12 and 18 days, respectively. They all started the work together, but A left after 3 days. In how many days was the remaining work completed? 

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  1. \(\frac{5}{2}\)
  2. \(\frac{9}{5}\)
  3. \(\frac{11}{4}\)
  4. 2

Answer (Detailed Solution Below)

Option 2 : \(\frac{9}{5}\)
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Given:

A can do the work in 9 days.

B can do the work in 12 days.

C can do the work in 18 days.

A, B, and C worked together for 3 days.

Formula used:

Total work = LCM of individual work days.

Efficiency = Total work / Individual work days.

Calculation:

Let the total work be 36 units.(LCM of 9, 12, and 18 = 36)

Efficiency of A = 36 / 9 = 4 units/day

Efficiency of B = 36 / 12 = 3 units/day

Efficiency of C = 36 / 18 = 2 units/day

Combined efficiency of A, B, and C = 4 + 3 + 2 = 9 units/day

Work done by A, B, and C in 3 days = 9 × 3 = 27 units

Remaining work = 36 - 27 = 9 units

Combined efficiency of B and C = 3 + 2 = 5 units/day

Time taken by B and C to complete the remaining work = 9 / 5

∴ The remaining work was completed in 9 / 5 days.

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