Chain Rule Q24

24. 30 labourers, working 7 hours a day can finish a piece of work in 18 days. If the labourers work 6 hours a day, then the number of labourers to finish the same piece of work in 30 days, will be:

[A] 15

[C] 22

[B] 21

[D] 25

Answer : B

Explanation :

Let the required number of laourers be x. Then,

Less working hrs / day, More Labourers (Indirect Proportion)

More days, Less Labourers (Indirect Proportion)

Working Hrs / Day 6 : 7 Days 30 : 18  :: 30 : x

6 x 30 x x = 7 x 18 x 30

6x = 126

x = 21