Aptitude - Time and Work - Discussion
Discussion Forum : Time and Work - General Questions (Q.No. 1)
1.
A can do a work in 15 days and B in 20 days. If they work on it together for 4 days, then the fraction of the work that is left is :
Answer: Option
Explanation:
| A's 1 day's work = | 1 | ; |
| 15 |
| B's 1 day's work = | 1 | ; |
| 20 |
| (A + B)'s 1 day's work = |  |
1 | + | 1 |  |
= | 7 | . |
| 15 | 20 | 60 |
| (A + B)'s 4 day's work = | |
7 | x 4 | |
= | 7 | . |
| 60 | 15 |
| Therefore, Remaining work = | |
1 - | 7 | |
= | 8 | . |
| 15 | 15 |
Discussion:
344 comments Page 24 of 35.
Kali said:
1 decade ago
1/15 = 4/60.
1/20 = 3/60.
Simply add 4+3 = 7.
And copy the denominator 60.
LCD:
15 = 5x3.
20 = 5x4.
LCD = 5x3x4 = 60.
1/20 = 3/60.
Simply add 4+3 = 7.
And copy the denominator 60.
LCD:
15 = 5x3.
20 = 5x4.
LCD = 5x3x4 = 60.
Krishna gummani said:
1 decade ago
A can do a work in 15 days.
B can do the work in 20 days.
i.e. in one day the work completed by A and B is 1/15 and 1/20 respectively.
In one day the work done by both A and B is, 1/15+1/20 = 7/60.
If, for one day the work done is 7/60, then for four days?
7/60*4 = 28/60.
The total work is 1.
Work done in 4 days is 28*60.
Then, remaining work is to be done is 1-28/60.
i.e. 8/15.
Hence proved.
B can do the work in 20 days.
i.e. in one day the work completed by A and B is 1/15 and 1/20 respectively.
In one day the work done by both A and B is, 1/15+1/20 = 7/60.
If, for one day the work done is 7/60, then for four days?
7/60*4 = 28/60.
The total work is 1.
Work done in 4 days is 28*60.
Then, remaining work is to be done is 1-28/60.
i.e. 8/15.
Hence proved.
Priya said:
1 decade ago
Is there any easy tricks to proceed further?
Prashant said:
1 decade ago
@Deepa.
Actually when fraction occur.
Then base must be same while doing it.
1/15 + 1/20 in this situation to calculate it base must be same. We can make it by multiply 1/15 By 4 and 1/20 By 3 so that it will be:
4/60 and 3/60 so.4/60 + 3/60 now we can do calculation result 7/60.
I hope you understand what I mean to say?
Actually when fraction occur.
Then base must be same while doing it.
1/15 + 1/20 in this situation to calculate it base must be same. We can make it by multiply 1/15 By 4 and 1/20 By 3 so that it will be:
4/60 and 3/60 so.4/60 + 3/60 now we can do calculation result 7/60.
I hope you understand what I mean to say?
Prathyusha said:
1 decade ago
Why we takes total work as 1?
ANURAG SAXENA said:
1 decade ago
LCM - 15, 20.
LCM = 60 UNIT.
A-- 15 DAY -60/15 = 4 U/D
B -- 20 DAY -60/20 = 3 U/D
A+B = 7 U/D.
4 DAYS = 7x4 = 28 U.
REAMING UNIT = 60-28 = 32 UNIT.
REAMING WORK = 32/60 = 8/15 DAYS.
LCM = 60 UNIT.
A-- 15 DAY -60/15 = 4 U/D
B -- 20 DAY -60/20 = 3 U/D
A+B = 7 U/D.
4 DAYS = 7x4 = 28 U.
REAMING UNIT = 60-28 = 32 UNIT.
REAMING WORK = 32/60 = 8/15 DAYS.
Rajesh said:
1 decade ago
Why (1 - 7/15) ?
What is total work as 1.
What is total work as 1.
Prasad said:
1 decade ago
(1/15+1/20) = 7/60.
Explanation:
15 = 5*3.
20 = 5*4.
Here the common nums are 3,4,5.
3*4*5 = 60.
60/15 = 4.
60/20 = 3.
(3/60+4/60) = 7/60.
Explanation:
15 = 5*3.
20 = 5*4.
Here the common nums are 3,4,5.
3*4*5 = 60.
60/15 = 4.
60/20 = 3.
(3/60+4/60) = 7/60.
Mahesh Gehlot said:
1 decade ago
7/60 is the total work done by A and B in day 1.
Therefore for 4 days we will calculate as below.
7/60 *4 means when its multiplication we will divide.
ie. 4/15 = 60 and we need to keep 7 integer as it was.
Therefore we get 7/15.
I don't know, Hope you'll understand this.
A simple logic when its + or - we will cross multiply
And when its * we will divide.
Thanks.
Therefore for 4 days we will calculate as below.
7/60 *4 means when its multiplication we will divide.
ie. 4/15 = 60 and we need to keep 7 integer as it was.
Therefore we get 7/15.
I don't know, Hope you'll understand this.
A simple logic when its + or - we will cross multiply
And when its * we will divide.
Thanks.
Latha said:
1 decade ago
Work done=>4*(1/15)+4*(1/20) = 7/15.
Remaining work = 1-7/15.
= 8/15.
Option D.
Remaining work = 1-7/15.
= 8/15.
Option D.
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