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:
164 comments Page 8 of 17.
Pooja Gowda said:
9 years ago
The total work is 100 unit.
A can do 80 unit in 20 days. So he can do 4 unit in 1 days.
Now A has finished 80 units so remaining work is 20 unit.
So, 20 unit work takes 3 days time to complete in which A will do 12 unit.
(since A do 4 unit/days).
Thus, B do 8 unit in 3 days.
And total work is 100 unit so B will take (3/8) * 100 = 37.5 days to complete total work.
A can do 80 unit in 20 days. So he can do 4 unit in 1 days.
Now A has finished 80 units so remaining work is 20 unit.
So, 20 unit work takes 3 days time to complete in which A will do 12 unit.
(since A do 4 unit/days).
Thus, B do 8 unit in 3 days.
And total work is 100 unit so B will take (3/8) * 100 = 37.5 days to complete total work.
Kriti said:
9 years ago
Hey guys 80/100 = 4/5 then why you people multiplying 5/4 * 20?
Ammus said:
9 years ago
80% of work will be completed int 20days. ie) 80/100 = 4/5.
Remaining 20% of work ie, 20/100 = 1/5.
A can do 100 % of work in 25 days,
So A's per day work is 1/25.
Now A+B together do the 20% of work.
(A + B) work = 3 days.
1/5 work = 3 work days.
1 work = 5 * 3 days,
Work = 15 days.
(A+B) per day work is = 1/15,
A's per day work is 1/25,
Now A + B = 1/15,
1/25 + B = 1/15,
B = 1/15 - 1/25,
B alone = 75/2 ie. 37 1/2 days.
Remaining 20% of work ie, 20/100 = 1/5.
A can do 100 % of work in 25 days,
So A's per day work is 1/25.
Now A+B together do the 20% of work.
(A + B) work = 3 days.
1/5 work = 3 work days.
1 work = 5 * 3 days,
Work = 15 days.
(A+B) per day work is = 1/15,
A's per day work is 1/25,
Now A + B = 1/15,
1/25 + B = 1/15,
B = 1/15 - 1/25,
B alone = 75/2 ie. 37 1/2 days.
Asma said:
9 years ago
Can anyone say why we are multiplying 20 with 5/4?
Wilson said:
9 years ago
A's 1 day work = 80% / 20 days
= 80/20
= 4 ( 4% work per day done by 'A' )
Remaining, (100 - 80) 20% work done by 'A' and 'B' in 3 days.
It means 'A' must have done 4% work per day, So, in 3 Days = 4% * 3.
= 4 * 3.
= 12.(12%work done by 'A' out of 20%).
Now, 8% (20-12) work done by 'B' in 3 Days.
Therefore, 'B' Alone can do Work = 100/8 * 3.
= 37 1/2 days.
= 80/20
= 4 ( 4% work per day done by 'A' )
Remaining, (100 - 80) 20% work done by 'A' and 'B' in 3 days.
It means 'A' must have done 4% work per day, So, in 3 Days = 4% * 3.
= 4 * 3.
= 12.(12%work done by 'A' out of 20%).
Now, 8% (20-12) work done by 'B' in 3 Days.
Therefore, 'B' Alone can do Work = 100/8 * 3.
= 37 1/2 days.
Sky said:
9 years ago
Well explained, Thank you @Baskar.
Satish said:
9 years ago
A - 20 - 80/100.
A - 1 - 80/(100 * 20) = 1/25.
A and B - 3 days = 20/100.
" 1 " = 20/(100 * 3).
= 1/15.
So,
1/15 -1/25 = 75/2.
A - 1 - 80/(100 * 20) = 1/25.
A and B - 3 days = 20/100.
" 1 " = 20/(100 * 3).
= 1/15.
So,
1/15 -1/25 = 75/2.
PrasadJadapalli said:
9 years ago
Super explanation @Snehagoud.
PrasadJadapalli said:
9 years ago
Super explanation @Snehagoud.
Jiya said:
9 years ago
Still, I'm not getting why its 5/4*20? Please explain briefly.
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