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A cistern is provided with two pipes A and B. A can fill it in 20 minutes and B can empty it in 30 minutes. If A and B be kept open alternately for one minute each, how soon will the cistern be filled ?
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- 121 minutes
- 110 minutes
- 115 minutes
- 120 minutes
- 121 minutes
Correct Option: C
As per the given in question , we have
| Part of the tank filled in first two minutes = | - | = | = | ||||
| 20 | 30 | 60 | 60 |
| ∴ Part of tank fillled in 114 minutes = | = | ||
| 60 | 20 |
∴ Remaining part of cistern will be filled in 115th minute
