Aptitude - Chain Rule - Discussion
Discussion Forum : Chain Rule - General Questions (Q.No. 5)
5.
39 persons can repair a road in 12 days, working 5 hours a day. In how many days will 30 persons, working 6 hours a day, complete the work?
Answer: Option
Explanation:
Let the required number of days be x.
Less persons, More days (Indirect Proportion)
More working hours per day, Less days (Indirect Proportion)
| Persons | 30 | : | 39 |  |
:: 12 : x |
| Working hours/day | 6 | : | 5 |
30 x 6 x x = 39 x 5 x 12
 x = |
(39 x 5 x 12) |
| (30 x 6) |
x = 13.
Discussion:
32 comments Page 4 of 4.
Rahul said:
1 decade ago
I always solve this as a work and time problem:
39 people working 5 hours a day finished 1/12th the work in 1 day.
39 people will therefore finish 1/60th (1/12 x 1/5) the work in 1 hour.
1 person will finish (1/60 x 1/39)th the work in 1 hour
So 30 people working for 6 hours will finish:
(1/60) x (1/39) x 6 x 30 = everything cancels out and you are left with 1/13th.
So: 30 people working for 6 hours will finish 1/13th the work in a day meaning they will take 13 days to finish.
39 people working 5 hours a day finished 1/12th the work in 1 day.
39 people will therefore finish 1/60th (1/12 x 1/5) the work in 1 hour.
1 person will finish (1/60 x 1/39)th the work in 1 hour
So 30 people working for 6 hours will finish:
(1/60) x (1/39) x 6 x 30 = everything cancels out and you are left with 1/13th.
So: 30 people working for 6 hours will finish 1/13th the work in a day meaning they will take 13 days to finish.
Jeyan said:
1 decade ago
Ya. Right. Even I got so!
Why not we say 39 persons did work in (12*5) hours.
Then what would be 30 persons working for (x*6) hours ?
Why not we say 39 persons did work in (12*5) hours.
Then what would be 30 persons working for (x*6) hours ?
Post your comments here:
Quick links
Quantitative Aptitude
Verbal (English)
Reasoning
Programming
Interview
Placement Papers