A contractor needs 2 men and 5 litres of paint to paint a fence wall,40m * 3m in 9hours. How many men and how much paint does he need to paint a fence wall 20m *12m in 3 hours. The men all work at same rate.

Answer 1

since the work needed is proportional to the area to be painted, he will need (20*12)/(40*3) = 2 times as much paint, or 10 liters.

If it takes the same time, he will need 2 times as many men, or 4 men.
But, since he wants it done in 1/3 the time, he will need 3 times as many men, or 12 men.