Aptitude - Time and Work - Discussion
Discussion Forum : Time and Work - General Questions (Q.No. 9)
9.
A does 80% of a work in 20 days. He then calls in B and they together finish the remaining work in 3 days. How long B alone would take to do the whole work?
23 days
37 days
37
40 days
Answer: Option
Explanation:
| Whole work is done by A in |  |
20 x | 5 |  |
= 25 days. |
| 4 |
| Now, | |
1 - | 4 | |
i.e., | 1 | work is done by A and B in 3 days. |
| 5 | 5 |
Whole work will be done by A and B in (3 x 5) = 15 days.
| A's 1 day's work = | 1 | , (A + B)'s 1 day's work = | 1 | . |
| 25 | 15 |
 B's 1 day's work = |
|
1 | - | 1 | |
= | 4 | = | 2 | . |
| 15 | 25 | 150 | 75 |
| So, B alone would do the work in | 75 | = 37 | 1 | days. |
| 2 | 2 |
Discussion:
168 comments Page 12 of 17.
Jiya said:
10 years ago
Still, I'm not getting why its 5/4*20? Please explain briefly.
Nagendran said:
10 years ago
Can anyone explain B's 1 day's work?
Muna sharma said:
10 years ago
How 80/100 can be 5/4? It should be 4/5.
Muna sharma said:
10 years ago
LCM of 15 and 25 is 150? Isn't it 75?
Rahul Berry said:
10 years ago
Thank you for your valid explanation @Baskar.
Jyoti said:
9 years ago
A does 80% work means 80÷100 =4/5 work in 20 days.
So, A's 1 day work = 4/5 * 1/20 = 1/25 work in 1day.
Now, It is said that A+B can do a piece of work in 3 days.
Therefore remaining work =1 - 4/5 = 1/5.
So, A+B's 1day work = 1/5 * 1/3 = 1/15.
Now work done by B in 1 day = 1/15-1/25 = 2/75.
Therefore B can do whole work in 75/2.
Hope it is clear to you!
So, A's 1 day work = 4/5 * 1/20 = 1/25 work in 1day.
Now, It is said that A+B can do a piece of work in 3 days.
Therefore remaining work =1 - 4/5 = 1/5.
So, A+B's 1day work = 1/5 * 1/3 = 1/15.
Now work done by B in 1 day = 1/15-1/25 = 2/75.
Therefore B can do whole work in 75/2.
Hope it is clear to you!
Sathyabama said:
9 years ago
Easy to understand it. Thanks @Wilson.
Manjunath deepak said:
9 years ago
A can do 80% of work in 20 days which means that he can do 100% work in 25 days.
A and B together can do 20% work in 3 days which means that they can do 100% work in 15 days.
Now,A's 1 day work=1/25--------->1/A=1/25.
(A+B)'s 1 day work=1/15------> (1/A)+(1/B)=1/15.
From the above two equations,(1/25)+(1/B)=1/15 which gives 1/B=2/75.
-->B=75/2=37.5.
A and B together can do 20% work in 3 days which means that they can do 100% work in 15 days.
Now,A's 1 day work=1/25--------->1/A=1/25.
(A+B)'s 1 day work=1/15------> (1/A)+(1/B)=1/15.
From the above two equations,(1/25)+(1/B)=1/15 which gives 1/B=2/75.
-->B=75/2=37.5.
Swapraj said:
9 years ago
80%= 4/5.
But, work done by A = 5/4 * 20 why not 4/5 * 20.
Please explain me.
But, work done by A = 5/4 * 20 why not 4/5 * 20.
Please explain me.
Manjunath Deepak said:
9 years ago
@Swapraj.
This is how it goes,
A---> 80% work--->20 days.
100% work---> How many days (say 'X' days).
Then you cross multiply it and you get the solution.
This is how it goes,
A---> 80% work--->20 days.
100% work---> How many days (say 'X' days).
Then you cross multiply it and you get the solution.
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