Well this is the easiest chapter to start with and one can easily attempt questions without using Paper-Pen.
The approach to solve questions revolves around finding work done per unit time i.e. work done in 1 day or 1 year or 1 hour.It depends upon the time unit given in the question.
For e.g.
Q. PM Modi visits 54 countries in 3 years. How many countries will he visit in 5 years ?
In this question year is the unit of time.
3 years -------------- 54 countries
1 year -------------- 54/3 = 18 countries (Efficiency)
Once we have this number 18 we can easily find that in 5 years he can visit 18*5 = 90 Countries
Secondly, Efficiency is inversely proportional to time
i.e. if Modi is thrice efficient than Manmohan it means that to do a piece of work Manmohan takes thrice as much time as Modi.
What to conclude ?
If Modi is thrice efficient as Mohan => Ratio of Time taken by Manhoman to Modi to dosame work is 3 : 1
If we use traditional method to find unit of घपला done in a single day
Lalu does 1/10 and Mulayam does1/15 unit of घपला in a day but now we have bloody fractions and that's irritating
Thus we need work done/day as integers
Work done/day for Lalu (X) = Total Work (घपला ) / No of days taken by Lalu (10)
Work done/day for Mulayam (Y) = Total Work (घपला ) / No of days taken by Mulayam (15)
To get X and Y as Integers, The Total Work (घपला ) should be divided by both 10 and 15
Thus it is best to take Total Work as LCM of 10,15 =30 (Not 150)
Work done/day for Lalu (X) = 30/10 = 3 units
Work done/day for Mulayam (Y) = 30/15 = 2 units
Now some questions :
Q. KRK is thrice as efficient as SRK. If SRK takes 30 days to finish a movie, in how many days can KRK do the same movie ?
Explanation : As Ratio of time taken taken by KRK to SRK is 1 : 3.Now SRK takes 30 days.
30 is 10 times 3 therefore same multiplication factor is applicable for KRK also.
Thus he will take 10 times 1 => 1*10= 10 Days
Q. BJP is thrice as good as Congress and passes a policy in 60 days less than Congress.Find the time in which BJP and Congress can pass a policy individually ?
Explanation : As Ratio of time taken taken by BJP to Congress is 1 : 3.
If we assume that BJP takes 1 unit of time and Congress takes 3 unit of time, then its difference will be 2 units.
But actual difference in question is given as 60 days which is 30 (Multiplication Factor) times 2.
therefore same multiplication factor (*30) is applicable for Individual times also.
Thus Congress takes 3 * 30 = 90 days and BJP takes 1 * 30 = 30 days to pass a policy
The approach to solve questions revolves around finding work done per unit time i.e. work done in 1 day or 1 year or 1 hour.It depends upon the time unit given in the question.
For e.g.
Q. PM Modi visits 54 countries in 3 years. How many countries will he visit in 5 years ?
In this question year is the unit of time.
3 years -------------- 54 countries
1 year -------------- 54/3 = 18 countries (Efficiency)
Once we have this number 18 we can easily find that in 5 years he can visit 18*5 = 90 Countries
Secondly, Efficiency is inversely proportional to time
i.e. if Modi is thrice efficient than Manmohan it means that to do a piece of work Manmohan takes thrice as much time as Modi.
What to conclude ?
If Modi is thrice efficient as Mohan => Ratio of Time taken by Manhoman to Modi to dosame work is 3 : 1
Using LCM to find Work done/unit Time
If Lalu does a घपला in 10 days and Mulayam does a घपला in 15 days.In how many days can they can do घपला together ?If we use traditional method to find unit of घपला done in a single day
Lalu does 1/10 and Mulayam does1/15 unit of घपला in a day but now we have bloody fractions and that's irritating
Thus we need work done/day as integers
Work done/day for Lalu (X) = Total Work (घपला ) / No of days taken by Lalu (10)
Work done/day for Mulayam (Y) = Total Work (घपला ) / No of days taken by Mulayam (15)
To get X and Y as Integers, The Total Work (घपला ) should be divided by both 10 and 15
Thus it is best to take Total Work as LCM of 10,15 =30 (
Work done/day for Lalu (X) = 30/10 = 3 units
Work done/day for Mulayam (Y) = 30/15 = 2 units
Q. KRK is thrice as efficient as SRK. If SRK takes 30 days to finish a movie, in how many days can KRK do the same movie ?
Explanation : As Ratio of time taken taken by KRK to SRK is 1 : 3.Now SRK takes 30 days.
30 is 10 times 3 therefore same multiplication factor is applicable for KRK also.
Thus he will take 10 times 1 => 1*10= 10 Days
Q. BJP is thrice as good as Congress and passes a policy in 60 days less than Congress.Find the time in which BJP and Congress can pass a policy individually ?
Explanation : As Ratio of time taken taken by BJP to Congress is 1 : 3.
If we assume that BJP takes 1 unit of time and Congress takes 3 unit of time, then its difference will be 2 units.
But actual difference in question is given as 60 days which is 30 (Multiplication Factor) times 2.
therefore same multiplication factor (*30) is applicable for Individual times also.
Thus Congress takes 3 * 30 = 90 days and BJP takes 1 * 30 = 30 days to pass a policy
Negative Work
It is the case when one person work but another destroys it.
For e.g. if Najeeb Jung appoints 30 IAS officers per day but Kejriwal Dismisses 10 IAS Officers per day.
Thus effective appointment is 30 -10=20 IAS Officers per day. In such questions our aim should be to find this effective rate first.
Let's us take a typical question.
Q. Tap A and Tap B can fill a bucket in 5 and 6 hours receptively but there is a leakage in Bucket which can empty it in 12 hours.If both the taps are opened together how much time will they take to fill the bucket ?
Sol.
Our overall objective is to find net water filled per hour.
To calculate this we need individual work done by both the taps as well as leakage per hour.
Thus we need Total work first = LCM ( 5,6,12) = 60
Thus Tap A does 60/5 =12 units Tap B does 60/6 = 10 units and Leakage does 60/12 = 5 units
Net Water filled per hour = 12+10-5 = 17
Time required = 60/17 hours
Sol.
Our overall objective is to find net water filled per hour.
To calculate this we need individual work done by both the taps as well as leakage per hour.
Thus we need Total work first = LCM ( 5,6,12) = 60
Thus Tap A does 60/5 =12 units Tap B does 60/6 = 10 units and Leakage does 60/12 = 5 units
Net Water filled per hour = 12+10-5 = 17
Time required = 60/17 hours
Q. Uma Bharti and Modi can clean Ganga in 30 days.[Biggest Joke of the millennium] They worked together for 20 days and then Modi left. After another 20 days, Uma finished the remaining work. In how many days Uma alone can finish the work (Actual answer is Never [LoL]) ?
Sol. Now Recall the steps
Step1 : Total Ganga to be cleaned : LCM of 30 and 20 = 60 units
Step2: Ganga cleaned by Uma and Modi in 1 day = 60/30=2 units
Step3: Ganga cleaned in 20 days = 2* 20 = 40 units
Then Modi left for a foreign visit to some Arab Nation this time
Step4: Ganga left to be clean = 60 - 40 = 20 units
Uma cleans 20 units of Ganga in 20 days
It means Uma cleans 1 unit of Ganga in 1 day
Step5 : To clean 60 units of Ganga she needs 60/1 = 60 days [Ans]
_________________________________________________________________________________
This was just the concept needed to attempt questions, you can try out questions at
http://www.indiabix.com/aptitude/time-and-work/029005
Happy Learning :)
Sol. Now Recall the steps
Step1 : Total Ganga to be cleaned : LCM of 30 and 20 = 60 units
Step2: Ganga cleaned by Uma and Modi in 1 day = 60/30=2 units
Step3: Ganga cleaned in 20 days = 2* 20 = 40 units
Then Modi left f
Step4: Ganga left to be clean = 60 - 40 = 20 units
Uma cleans 20 units of Ganga in 20 days
It means Uma cleans 1 unit of Ganga in 1 day
Step5 : To clean 60 units of Ganga she needs 60/1 = 60 days [Ans]
_________________________________________________________________________________
This was just the concept needed to attempt questions, you can try out questions at
http://www.indiabix.com/aptitude/time-and-work/029005
Happy Learning :)
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