A and B can complete a piece of work in 18 days and 12 days, respectively. They work on alternate days till the work gets completed. How long (in days) would it take A and B to complete the work, starting with A on the first day?

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SSC GD Constable (2022) Official Paper (Held On : 13 Jan 2023 Shift 1)
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  1. 15 days
  2. 14 days
  3. 16 days 
  4. 14.5 days 

Answer (Detailed Solution Below)

Option 4 : 14.5 days 
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Detailed Solution

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Given:

A can do a piece of work in 18 days

B can do a piece of work in 12 days 

Formula Used:

Efficiency = Total work/No. of days

Calculation:

Total work be ( L.C.M of 18, 12) be 36 unit.

Efficiency of A  = work done by A in 1 day = 36/18 = 2 

Efficiency of B = work done by B in 1 day = 36/12 = 3

Now, work done in 2 days = 5 

So, in 7 pair of 2 days they will complete 7 × 5 = 35 unit of work 

In 14 days 35 unit of work is done 

Remaining work = (36 - 35 ) = 1 unit 

As, they work alternately with A as first .So, on 15th day remaining 1 unit of work will be done by A in .5 day.

So, No. of days taken to complete the whole work = 14.5 days

Hence, A and B takes 14.5  days to complete the work.

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