A can do a piece of work in 7 days of 9 hr each, and B can do it in 6 days of 7 hr each. How long will they take to do it working together \frac{42}{5} hr a day ?

Foundation

Mathematics Foundation

Time Speed Distance

Question

A can do a piece of work in 7 days of 9 hr each, and B can do it in 6 days of 7 hr each. How long will they take to do it working together $\frac{42}{5}$ hr a day ?

4 days

4.5 days

None

3 days

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A takes 7 × 9 = 63 hr.

In 1hr A does = $\frac{1}{63}$ of work

B takes 6 × 7 = 42 hr

In 1 hr B does = $\frac{1}{42}$ of work

Work of 1 hr A + B in $(\frac{1}{63} + \frac{1}{42})$

A + B in $\frac{42}{5} hr = (\frac{1}{63} + \frac{1}{42}) \times \frac{42}{5}$

= $\frac{105}{2646} \times \frac{42}{5} = \frac{4410}{13230} = 0 .33$

Number of days = $\frac{1}{0.33}$ = 3.

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