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 12 of 17.
Himanshu gawande said:
1 decade ago
A's 1 day work (1/80%)x20 = 25 days.
Sudheer said:
1 decade ago
A's 80% work i.e 4/5 work = 20 days.
Therefore 1 work = 20x5/4 = 25 days.
Similarly, (A+B) 's remaining work i.e 20% work==>1/5 work = 3 days.
Therefore 1 work = 5x3 = 15 days.
We got A = 1/25.
And A+B = 1/15.
Solve above equations we will get B = 75/2.
Therefore 1 work = 20x5/4 = 25 days.
Similarly, (A+B) 's remaining work i.e 20% work==>1/5 work = 3 days.
Therefore 1 work = 5x3 = 15 days.
We got A = 1/25.
And A+B = 1/15.
Solve above equations we will get B = 75/2.
Juanita said:
1 decade ago
My understanding is that A alone does 80% work which is 5/4. Remaining 20% work is done by A & B which is 1/5.
Rapaka said:
1 decade ago
80%-----20 days.
100%------?
100%-20/80 = 25 days this is A work.
Now,
100%----25.
20%-----?
Answer 5 since it been done by A+B in 3 days 5x3 = 15 days.
If we subtract B from A+B that would be the answer.
1/15-1/25 = 4/150 = 2/75.
Hens option C.
100%------?
100%-20/80 = 25 days this is A work.
Now,
100%----25.
20%-----?
Answer 5 since it been done by A+B in 3 days 5x3 = 15 days.
If we subtract B from A+B that would be the answer.
1/15-1/25 = 4/150 = 2/75.
Hens option C.
Sam said:
1 decade ago
Solution.
A's 1 day work = (80/100)*(1/20) = (1/25).
(A+B) 's 1 day work = (20/100)*(1/3) = (1/15).
So B's 1 day work will be (A+B) - (A).
B's 1 day work will be (2/75).
Hence 1 work will be completed by B alone in (75/2) days that's option C.
A's 1 day work = (80/100)*(1/20) = (1/25).
(A+B) 's 1 day work = (20/100)*(1/3) = (1/15).
So B's 1 day work will be (A+B) - (A).
B's 1 day work will be (2/75).
Hence 1 work will be completed by B alone in (75/2) days that's option C.
Raaj said:
1 decade ago
80% = 120.
100% = 150.
A can do 120 unit in 20 days.
A can do 1 day = 120/20 = 6 unit.
Remaining 150- 120 = 30.
A+B can do 30 unit in 3 day.
A+B can do in 1 day = 30/3 = 10 unit.
A+ B = 10 unit.
A = 6 unit.
B = 10 - 6= 4 unit.
B can alone do = 150 / 4 = 37 1/2.
100% = 150.
A can do 120 unit in 20 days.
A can do 1 day = 120/20 = 6 unit.
Remaining 150- 120 = 30.
A+B can do 30 unit in 3 day.
A+B can do in 1 day = 30/3 = 10 unit.
A+ B = 10 unit.
A = 6 unit.
B = 10 - 6= 4 unit.
B can alone do = 150 / 4 = 37 1/2.
Manjula said:
1 decade ago
Awesome explanation by @Bhaskar and @Rajendra.
Umadatla said:
1 decade ago
1/15-1/25 = 2/75.
How you got 5 1/75?
How you got 5 1/75?
Mayuri said:
1 decade ago
A's 1 day work = 1/20*80/100.
= 1/25.
A+B 1 day work = 1/3*20/100.
= 1/15.
A+B-A=B'S 1 day work = 1/25-1/15.
= 1/75.
= 37 1/2.
Simple.
= 1/25.
A+B 1 day work = 1/3*20/100.
= 1/15.
A+B-A=B'S 1 day work = 1/25-1/15.
= 1/75.
= 37 1/2.
Simple.
Bipinvvijayan@gmail.com said:
1 decade ago
Let us say that the work is of 100 units then A finishes 80 units in 20 days which means 80/20 = 4 units per day.
Remaining work = 20 units.
Units finished per day = 4 + B.
Days taken = 3 = 20/(4 + B) = 12 + 3B = 20.
3B = 8.
B = 8/3.
If B finishes 8/3 units every day then to finish 100 units B will take 100 x 3/8 = 37.5 days.
Remaining work = 20 units.
Units finished per day = 4 + B.
Days taken = 3 = 20/(4 + B) = 12 + 3B = 20.
3B = 8.
B = 8/3.
If B finishes 8/3 units every day then to finish 100 units B will take 100 x 3/8 = 37.5 days.
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