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A, B and C can do a piece of work in 30, 20 and 10 days respectively. A is assisted by B on one day and by C on the next day, alternately. How long would the work take to finish ?
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9 8 days 3 -
4 8 days 8 -
8 4 days 13 -
9 1 days 13
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Correct Option: A
Work done in first two days
| = | + | + | ||||
| 30 | 20 | 10 |
| = | + | + | ||||
| 15 | 20 | 10 |
| = | = | |||
| 60 | 60 |
| Work done in first 8 days = | 60 |
Remaining work
| = 1 - | = | = | ||||
| 60 | 60 | 15 |
(A + B)’s 1 day’s work
| = | + | = | = | |||||
| 30 | 20 | 60 | 12 |
| ∴ Remaining work = | - | |||
| 15 | 12 |
| = | = | = | ||||
| 60 | 60 | 20 |
(A + C)’s 1 day’s work
| = | + | = | = | |||||
| 30 | 10 | 30 | 15 |
| ∴ Time taken = | × | |||
| 20 | 2 |
| = | day | 8 |
| Total time = 9 + | = 9 | days | ||
| 8 | 8 |
