3 men can build a stage in 18 days while 6 boys can also do it in 18 days. If 4 men and 4 boys work on the assignment together, how many days will they take to finish it?
4.5
6
9
21
Explanation:
Men = M; Days = D; Time/Hours = T; Work = W
M1D1T1W2 = M2D2T2W1
Note that - W2 is on left side and W1 is on right side
To complete work in 18 days we need either 3 men or 6 boys.
∴ 1 man = 2 boys
Take work done = 1
∴ 3 men x 18 days x 1 = (4 men + 4 boys) x ? days x 1
Remember - Convert either all men to boys or all boys to men.
∴ 6 boys x 18 days x 1 = (8 boys + 4 boys) x ? days x 1
∴ ? = 9 days = they will need these many days