• This is one of the easiest concepts in quantitative aptitude and questions on this topic are frequently asked in bank PO exams. As answering these questions boosts one’s score, it is important for a candidate to master this concept.
• The word ‘unit’ means one and this method is about finding for ‘one’. Generally questions come in such a way that you are given work done by x people and you are asked work done by y people.
• If two variables are related in such a way that the increase in one variable causes a proportional increase in the other, then such variables are said to be in direct proportion. For example, the more the number of people working on a job, the more is the work done per unit time.
• If two variables are related in such a way that the increase in one variable causes a proportional decrease in the other, then such variables are said to be in indirect proportion. For example the more the number of people working on a job, the less is the time taken to complete the job.
• In questions that involve three variables, the recommended approach is to consider each variable individually and then take all the variables into account.
Question) Four women take 3 hours to complete 40% of a work. How many additional women are required if the work had to be completed in 6 hours?
Solution) Time taken by 4 women to complete 40% work = 3hrs
Time taken by 4 women to complete 100% work = 3*2.5 = 7.5 hrs
4 women complete the work in 7.5 hours => Units of work = 4*7.5 = 30
x women complete the work in 6 hrs => x = 30/6 = 5 women
Therefore additional women required = 5-4 = 1
Question) 5 men can repair 25 air-conditioners in 20 days. How long will 10 men take to repair 100 air-conditioners?
Solution) If 5 men can repair 25 air-conditioners in 20 days, then 1 man can repair 5 air-conditioners in 20 days.
If 1 man can repair 5 air conditioners in 20 days, then 1 man can repair 100 air-conditioners in 20*20 = 400 days.
If 1 man can repair 100 air-conditioners in 400 days, then 10 men can repair 100 air-conditioners in 400/10 = 40 days.