Join 60,000+ competitive exam aspirants
If 6 men and 8 boys can do a piece of work in 10 days while 26 men and 48 boys can do the same work in 2 days, then the time taken by 10 men and 20 boys for doing the same piece of work will be:
3 days
5 days
4 days
2 days
5 days
Equate the total man-days for both cases to find the efficiency ratio between a man and a boy, then substitute into the target equation.
6 men and 8 boys can do the work in 10 days, 26 men and 48 boys can do the same work in 2 days
(6M+8B)├Ч10=(26M+48B)├Ч2
Equate the total man-days for both cases to find the efficiency ratio between a man and a boy, then substitute into the target equation.
Multiplying the number of days incorrectly or mixing up the efficiency ratio of men and boys.
Step 1: Set up the work equation
Since total work remains constant, the product of workers and days in both cases is equal: (6M+8B)├Ч10=(26M+48B)├Ч2
60M+80B=52M+96B
Step 2: Find the efficiency ratio of Men to Boys
Simplify the equation to find the relation between a man (M) and a boy (B): 60MтИТ52M=96BтИТ80BтЯ╣8M=16BтЯ╣M=2B
1┬аman=2┬аboys
Step 3: Calculate Total Work in units
Substitute M=2B into the first case expression: Total┬аWork=(6(2B)+8B)├Ч10=(12B+8B)├Ч10=20B├Ч10=200┬аunits
Total┬аWork=200┬аunits
Step 4: Find efficiency of the target group and calculate time
The target group consists of 10 men and 20 boys: Efficiency=10(2B)+20B=20B+20B=40BTime=40200тАЛ=5┬аdays
5┬аdays
D is correct because the calculated time taken by 10 men and 20 boys to complete the work is 5 days.
This same proportionality concept is widely used in Pipes & Cisterns and Speed, Time & Distance problems involving mixed groups.