Best trick that I use in exams myself is by finding the efficiency of workers in percent. If A can do a job in 2 days then he can do 50% in a day.
| Number of days required to complete the work | Work that can be done per day | Efficiency in Percent |
|---|---|---|
| n | 1/n | 100/n |
| 1 | 1/1 | 100% |
| 2 | 1/2 | 50% |
| 3 | 1/3 | 33.33% |
| 4 | 1/4 | 25% |
| 5 | 1/5 | 20% |
| 6 | 1/6 | 16.66% |
| 7 | 1/7 | 14.28% |
| 8 | 1/8 | 12.5% |
| 9 | 1/9 | 11.11% |
| 10 | 1/10 | 10% |
| 11 | 1/11 | 9.09% |
Now let's solve questions with this trick
Question - A take 5 days to complete a job and B takes 10 days to complete the same job. In how much time they will complete the job together ?
Solution - A's efficiency = 20%, B's efficiency = 10%. If they work together they can do 30% of the job in a day. To complete the job they need 3.33 days.
Question - A is twice as efficient as B and can complete a job 30 days before B. In how much they can complete the job together ?
Solution - Let efficiency percentage as x
A's efficiency = 2x and B's efficiency = x
A is twice efficient and can complete the job 30 days before B. So,
A can complete the job in 30 days and B can complete the job in 60 days
A's efficiency = 1/30 = 3.33%
B's efficiency = 1/60 = 1.66%
Both can do 5% ( 3.33% + 1.66% ) of the job in 1 day.
So the can complete the whole job in 20 days (100/5)
Question - A tank can be filled in 20 minutes. There is a leakage which can empty it in 60 minutes. In how many minutes tank can be filled?
Solution -
Method 1
⇒ Efficiency of filling pipe = 20 minutes = 1/3 hour = 300%
Method 1
⇒ Efficiency of filling pipe = 20 minutes = 1/3 hour = 300%
⇒ Efficiency of leakage = 60 minutes = 100%
We need to deduct efficiency of leakage so final efficiency is 200%. We are taking 100% = 1 Hour as base so answer is 30 minutes.
Update - 09-09-2013 ( As Shobhna and Aswin are facing problem in solving this question, I am solving this question with second method which is also very easy, hope this will make the solution lot easier.)
Method 2
⇒ Efficiency of filling pipe = 100/20 = 5%
⇒ Efficiency of leakage pipe = 100/60 = 1.66%
⇒ Net filling efficiency = 3.33%
So tank can be filled in = 100/3.33% = 30 minutes
Update - 09-09-2013 ( As Shobhna and Aswin are facing problem in solving this question, I am solving this question with second method which is also very easy, hope this will make the solution lot easier.)
Method 2
⇒ Efficiency of filling pipe = 100/20 = 5%
⇒ Efficiency of leakage pipe = 100/60 = 1.66%
⇒ Net filling efficiency = 3.33%
So tank can be filled in = 100/3.33% = 30 minutes
You can change the base to minutes or even seconds.
You can solve every time and work question with this trick. In above examples I wrote even simple calculations. While in exams you can do these calculations mentally and save lots of time.
You can find more tricks like this in quantitative aptitude section.
Comment below in case of any query, I promise to reply within 24 hours.
Update 09 October 2013 - Question requested by Chitra Salin
Comment below in case of any query, I promise to reply within 24 hours.
Update 09 October 2013 - Question requested by Chitra Salin