P can do a work in 10 days. Q can do the same work in 15 days. If they work together for 5 days, how much of the work will they complete?
P's 1 day work = $$\frac{1}{10}$$
Q's 1 day work = $$\frac{1}{15}$$
(P+Q)'s 1 day work = $$\frac{1}{10}+\frac{1}{15}=\frac{1}{6}$$
(P+Q)'s 5 days work = $$5\times\frac{1}{6}=\frac{5}{6}$$
So, they will complete $$\frac{5}{6}$$ of the work.
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