A can do a piece of work in 25 days and B can do it in 20 days. They work together for 5 days and then A goes away. How many more days will B require to finish the work?
A9 days
B10 days
C11 days
D12 days
Answer & Solution
Correct answer: C. 11 days
A's one-day work is $1/25$ and B's is $1/20$. Together they do $1/25+1/20=9/100$ of the work per day, so in 5 days they complete $5\times 9/100=9/20$. The remaining work is $1-9/20=11/20$. Since B alone does $1/20$ per day, he needs $(11/20)\div(1/20)=11$ days.
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