Abha can do some work in 10 days, Billu can do it in 20 days and Chintu can do it in 40 days. They start working in turns with Abha starting to work on the first day followed by Billu on the second day and by Chintu on the third day and again by Abha on the fourth day and so on, till the work is completed fully. Find the time taken (approx.) to complete the work fully.

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  1. 16 days
  2. 15 days 
  3. 17 days
  4. 20 days

Answer (Detailed Solution Below)

Option 1 : 16 days
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Given:

Abha can complete the work in 10 days

Billu in 20 days

Chintu in 40 days

Calculation:

Take LCM of 10, 20, and 40 to assume total work = 40 units (LCM method)

Work per day:

Abha: 40 ÷ 10 = 4 units/day

Billu: 40 ÷ 20 = 2 units/day

Chintu: 40 ÷ 40 = 1 unit/day

Work in 3-day cycle:

Day 1 (Abha) + Day 2 (Billu) + Day 3 (Chintu) = 4 + 2 + 1 = 7 units in 3 days

Full 5 cycles (15 days) → 5 × 7 = 35 units

Remaining work = 40 − 35 = 5 units

Next day (Day 16) → Abha works = 4 units → total = 39 units

Next day (Day 17) → Billu works = 2 units, but only 1 unit left → he needs only 0.5 day

Total time taken = 16 full days + 0.5 day = 16.5 days ≈ 16 days

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