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A can do in one day three times the work done by B in one day. They together finish 2/5 of the work in 9 days. The number of days by which B can do the work alone is :
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- 90 days
- 120 days
- 100 days
- 30 days
Correct Option: A
Let time taken by A alone in doing work be x days.
∴ Time taken by B alone = 3x days
| ∵ A and B together finish | work in 9 days. | 5 |
∴ TIme taken by A and B in doing whole work
| = | = | days | ||
| 2 | 2 |
| = | + | = | ||||
| x | 3x | 45 |
| ⇒ | = | |||
| 3x | 45 |
| ⇒ | = | ⇒ 2 × 3x = 4 × 45 | ||
| 3x | 45 |
| ⇒ x = | = 30 days | 2 × 3 |
∴ Time taken by B = 3x days = 3 × 30 = 90 days
Aliter : Using Rule 22,
Here, n = 3 and D
| = | = | days | ||
| 2 | 2 |
(Time taken to finish whole work)
Time taken by B = (n + 1)D
| = (3 + 1) × | = 90 days | 2 |
