If 10 men can do a piece of work in 12 days, how many men are needed to do the same work in 8 days?
Answer: B
This is a man-days problem. We use the formula M1*D1 = M2*D2. Given M1=10, D1=12, D2=8. \(10 \times 12 = M2 \times 8 \Rightarrow 120 = 8 \times M2 \Rightarrow M2 = 120/8 = 15\). So, 15 men are needed.