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A can do a piece of work in 20 days while B alone can do In 12 days. B worked at it for 9 days. A can finish the remaining work in 

A. 3 days 

B. 5 days 

C. 7 days 

D. 11 days

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Number of days A required do a piece of work : 20

Number of days B required do a piece of work : 12

Work done by A in one day: \(\frac{1}{20}\)

Work done by B in one day: \(\frac{1}{12}\)

B works alone for 9 days, so work completed by B in 9 days : \(9\times\frac{1}{12}=\frac{3}{4}\)

Work left = \(1-\frac{3}{4}=\frac{1}{4}\)

But \(\frac{3}{4}\)th of the work is already done by B

∴ Time required to complete the remaining \(\frac{1}{4}\)th of the work by A : \(\frac{1}{4}\times20\) = 5 days

∴ Time taken to finish the work 9 + 5 = 14 days

∴ A can finish the remaining work in : 5 days

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