1.

A and B can do a piece of work in 6 days and 4 days respectively. A started the work, worked at it for 2 days and then was joined by B. Find the total time taken to complete the work.

Answer»

Given, 

A can do a piece of work in = 6 days

 B can do same piece of work in = 4 days

∵ Work done by A in 1 day \(=\frac{1}{6}\)

∴ In 2 Days he finished \(={2}\times\frac{1}{6}=\frac{1}{3}\) part of work 

Remaining work \(={1}-\frac{1}{3}=\frac{2}{3}\)

So, Remaining work will be finished by A and B in \(\frac{\frac{2}{3}}{\left\{ \frac{1}{6}+\frac{1}{4}\right\}}=\)\(\frac{\frac{2}{3}}{\frac{5}{12}}=\frac{2\times12}{5\times3}=\frac{8}{5}={1}\frac{3}{5}\) days

∴ Total time taken to complete the work \(={2}+{1}\frac{3}{5}={3}\frac{3}{5}\) days



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