BECE Mathematics 2016 Paper

Concept:The same amount of work is done, so the number of boys and the time taken are inversely proportional.Explanation:Total work can be calculated as boys multiplied by time.Total work $= 15 \times 12 = 180$ boy-hours.This total work remains the same for 9 boys.Let the required time be $t$ hours.Then, $9 \times t = 180$.Divide both sides by 9:$t = \frac{180}{9} = 20$.So, 9 boys will take 20 hours to weed the plot.Answer:D. 20 hours