P and Q can do work separately in 10 and 20 days, respectively. In how many days can they finish it, working together?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 20/3
A person who finishes a job in \(n\) days does \(\frac{1}{n}\) of it in one day, and when two people work together their one-day work is added.
P’s one-day work \(=\frac{1}{10}\); Q’s one-day work \(=\frac{1}{20}\)
Together in one day: \(\displaystyle \frac{1}{10}+\frac{1}{20}=\frac{2+1}{20}=\frac{3}{20}\) of the work
Days to finish the whole work \(\displaystyle =1\div\frac{3}{20}=\frac{20}{3}\), that is, \(6\frac{2}{3}\) days