TIME AND WORK
The concept of time and work is important topic for the aptitude exams. Questions on this chapter have been appearing regularly over the past decade in all aptitude exams. In this topic we discuss about relation between Time and Work and Pipes and Cisterns.
Relation Between Time and Work
Consists of problems on time taken to do a certain job by certain number of workers
• The change in the number of hours required to do the job if the number of workers are changed.
• The number of hours required to do the same job by different people either of same and different efficiency.
Some Important Points
• Work done is directly proportional to number of men.
• Work done is also depends on number of day people work.
• People work for less number of days less work will be done and people work for more number of days more work will be done.
• Work done is also proportional to number of hours.
• The work done is directly proportional to efficiency.
Combine of all these we get,
N1*D1*H1*n1/W1 = N2*D2*H2*n2/W2
W = K * N * D * H * n
Where W = Work done
N = Number of men
D = Number of days
H = Number of hours per day
n = Efficiency
K = Constant
Efficiency
Efficiency is directly proportional to the work done and inversely proportional to the time taken.
Efficiency = Work / Time
Important Concepts
• If A can complete the work in 10 days, then in one day A will be doing 1 / 10 of the total work.
• If efficiency of A is twice that that of B then,
- In a given amount of time A will be able to twice the work as compare to B. (2:1)
- If the same work needs to be completed, then A will take half of the time when compared to time taken by B. (1:2)
PIPES AND CISTERNS
Consists of problems on how long it will take for different pipes of same/varying diameters to fill a cistern (Tank).
• The change in the number of hours required to fill a cistern if the number of pipes are changed.
• The number of hours required to fill the same cistern by different pipes of same/varying diameters either of same and different flow rates.
Important Concepts
If a pipe can fill a tank in x hours and another pipe can fill a tank in y hours, then the fraction of tank filled by both the pipes together in 1 hours
1/x + 1/y
(x+y) / xy
Or, the time required to fill the tank by both pipes
= (xy) / (x+y)
If a pipe can fill a tank in x hours and another pipe can empty the fill tank in y hours, then the fraction of tank filled by both the pipes together in 1 hours
1/x - 1/y
(x-y) / xy
Or, the time required to fill the tank by both pipes
= xy / (x-y)
ALL THE BEST!!!!
