Question

A can do a piece of work in 20 days and B in 15 days. They worked together on it for 6 days and then A left. How long will B take to finish the remaiing work?

Answer 1

A can do a piece of work in = 20 days
B can do a piece of work in = 15 days
$\therefore$ A's 1 day work $=\frac{1}{20}$
B's 1 day work $=\frac{1}{15}$
(A + B)'s 1 day work $=\frac{1}{20}+\frac{1}{15}$
$=\frac{3+4}{60}=\frac{7}{60}$
(A + B)'s 6 days work $=\frac{7}{60}\times 6=\frac{7}{10}$
Remaining Work $=1-\frac{7}{10}$
$=\frac{10-7}{10}=\frac{3}{10}$
B can do 1 work in = 15 days.
B can do $\frac{3}{10}$ work in $=15\times \frac{3}{10}$ days.
$=\frac{45}{10}$ days $=\frac{9}{2}$ days $=4\frac{1}{2}$ days.