Suppose $A$ alone can finish a piece of work in $15$ days and $B$ alone can do it in $20$ days. If both of them together, how much time will they take to finish it?

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Solution

We can apply formula $\frac{m n}{m + n}$ . Here $m = 15$ days and $n = 20$ days. We know that A and B together finish the work in $\frac{m n}{m + n}$ days. Substituting $m = 15$ and $n = 20$ , we get
$\frac{m n}{m + n} = \frac{20 \times 15}{20 + 15} = \frac{300}{35} = 8 \frac{4}{7}$ .
Thus A and B together finish the work in $8 \frac{4}{7}$ days.

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Suppose A alone can finish a piece of work in 15 days and B alone can do it in 20 days. If both of them together, how much time will they take to finish it?

We can apply formula mnm+n . Here m=15 days and n=20 days. We know that A and B together finish the work in mnm+n days. Substituting m=15 and n=20, we getmnm+n=20×1520+15=30035=847.Thus A and B together finish the work in 847 days.

Suppose $A$ alone can finish a piece of work in $15$ days and $B$ alone can do it in $20$ days. If both of them together, how much time will they take to finish it?