If 20 persons can do a work in 15 days, then how many more persons are required to do it in 10 days?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 10
The total work is fixed, so persons × days stays the same: to finish in fewer days, more persons are needed. The question asks how many more persons, so the present 20 are taken away at the end.
Total work, in person-days: \(20\times15=300\)
Persons needed to finish in 10 days: \(\frac{300}{10}=30\)
Extra persons needed: \(30-20=10\)