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Worker $A$ takes $8$ hours to do a job. Worker $B$ takes $10$ hours to do the same job. How long it take both $\text{A&B}$, working together but independently, to do the same job?

  1. $40/9$ days
  2. $40/7$ days
  3. $7.5$ days
  4. $8.5$ days
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Answer is A

A =$\frac{1}{8}$        $B=\frac{1}{10}$

We have to find  A+B = $\frac{1}{8} +\frac{1}{10} = \frac{9}{40}$

Time taken for both A and B to do the same work is $\frac{40}{9}$ hours

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