If 3 men or 9 boys can finish a work in 21 days, then in how many days can 5 men and 6 boys finish the same work?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 9
“3 men or 9 boys” do the same work in the same time, so 3 men do as much as 9 boys, that is, 1 man = 3 boys. The whole team is then counted in boys.
5 men and 6 boys \(=5\times3+6=21\) boys
Total work \(=9\) boys \(\times\) 21 days \(=189\) boy-days
Days for 21 boys \(=189\div21=9\)