A and B can complete a task together in 9 days. A by herself can complete the task in 12 days. How many days will B need to complete the task alone?

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MP Excise Constable Official paper (Held On: 20 Feb 2023 Shift 3)
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  1. 48 days
  2. 24 days
  3. 36 days 
  4. 12 days 

Answer (Detailed Solution Below)

Option 3 : 36 days 
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MP Excise Constable Full Test 1
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Detailed Solution

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Given:

A and B can complete a task together in 9 days.

A alone can complete the task in 12 days.

Formula used:

Work rate of A and B together = Work rate of A + Work rate of B

Work rate is given by the reciprocal of the number of days taken to complete the task.

Calculation:

Work rate of A and B together = 1/9

Work rate of A = 1/12

Let the work rate of B be 1/B

⇒ 1/9 = 1/12 + 1/B

⇒ 1/B = 1/9 - 1/12

⇒ 1/B = (4 - 3) / 36

⇒ 1/B = 1/36

⇒ B = 36

∴ The correct answer is option (3).

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