If 40 men can build a wall 300 m long in 12 days working 6 hours a day, how long will it take 30 men to build a similar wall 200 m long working 8 hours a day ?
Answer: B. 8 days
40 men can build 300 m long wall working 6 hour a day in = 12 days. 1 man can build 1 m long wall working 1 hour a day in = ${12 × 6 × 40} /300$ 30 men can build 200 m long wall working 8 hour a day in = ${12 × 6 × 40 × 200}/{300 × 8 × 30}$ = 8 days.