Question

two men can do a piece of work in 6 hour and 4 hours respectively after the first has worked for two hours he joined by the other by when should the work be completed

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Answer 1

The time taken by them together = $\frac{1}{\frac{1}{6} + \frac{1}{4}} = \frac{12}{5}$

After the first person worked for two hours, $\frac{1}{3}$ of the work was completed.

So, $\frac{2}{3}$ of the work was left.

Time taken = $\frac{2}{3} \times \frac{12}{5} = \frac{8}{5} hours$