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A and B can do a piece of work in 15 days. B and C can do the same work in 10 days and A and C can do the same in 12 days. Time taken by A, B and C together to do the job is
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- 4 days
- 9 days
- 8 days
- 5 days
Correct Option: C
| (A+B)’s 1 day’s work = | 15 |
| (B+C)’s 1 day’s work = | 10 |
| (A+C)’s 1 day’s work = | 12 |
On adding all three,
2(A+B+C)’s 1 day’s work
| = | + | + | = | |||||
| 15 | 10 | 12 | 60 |
| = | = | |||
| 60 | 4 |
| ∴ (A + B + C)’s 1 day’s work = | 8 |
∴ Required time = 8 days
Aliter : Using Rule 5,
| Time taken = | xy + yz + zx |
| = | 15 × 10 + 10 × 12 + 12 × 15 |
| = | 150 + 120 + 180 |
| = | = 8 days | 450 |
