Aptitude - Time and Work - Discussion
Discussion Forum : Time and Work - General Questions (Q.No. 16)
16.
X and Y can do a piece of work in 20 days and 12 days respectively. X started the work alone and then after 4 days Y joined him till the completion of the work. How long did the work last?
Answer: Option
Explanation:
| Work done by X in 4 days = |  |
1 | x 4 |  |
= | 1 | . |
| 20 | 5 |
| Remaining work = | |
1 - | 1 | |
= | 4 | . |
| 5 | 5 |
| (X + Y)'s 1 day's work = | |
1 | + | 1 | |
= | 8 | = | 2 | . |
| 20 | 12 | 60 | 15 |
| Now, | 2 | work is done by X and Y in 1 day. |
| 15 |
| So, | 4 | work will be done by X and Y in | |
15 | x | 4 | |
= 6 days. |
| 5 | 2 | 5 |
Hence, total time taken = (6 + 4) days = 10 days.
Discussion:
68 comments Page 3 of 7.
Inna Reddy Chilakala said:
10 years ago
Total work = X.
A = X (begin the work and he is in End of the work).
B = X-4 (After 4 days he joined).
= X/20 + X - 4/12 = 1.
= 3X + 5X - 20/60.
8X = 80.
X = 10.
A = X (begin the work and he is in End of the work).
B = X-4 (After 4 days he joined).
= X/20 + X - 4/12 = 1.
= 3X + 5X - 20/60.
8X = 80.
X = 10.
Sachin said:
9 years ago
Please help me to understand this, why we took 15/2 instead of 2/15?
Thank in advance.
Thank in advance.
Patel Komal said:
9 years ago
Please help me to get this, why you take (1/20 * 4)?
Makvana Disha said:
9 years ago
@Sachin,
2/15 = 1 day work.
Then for remaining work 4/5 = ?
i.e. (4/5) * (15/2) = 6 days.
Total days are, 6 + 4 = 10 days.
2/15 = 1 day work.
Then for remaining work 4/5 = ?
i.e. (4/5) * (15/2) = 6 days.
Total days are, 6 + 4 = 10 days.
Nik said:
9 years ago
But here it asked like "how long did they work", why should we consider A's work here?
Inba said:
7 years ago
How come 4/5?
Please explain.
Please explain.
Priya said:
8 years ago
One shortcut method.
Total work assumes as 1unit.
Use option to Slove this
1.we know that x's 1day work= 1/20.
Same y's=1/12
Choose option no. a, i.e .6 if x work for 6 days so y work for 2 days because y start working after 4 days so.
6/20+2/12 = 1,
Is not equal to 1.
So, the answer is not 6.
Take another i.e.10.
If x takes 10 days, y takes 6 days.
10/20+6/12 = 1.
Lhs=rhs . So the ans. Is 10days.
Total work assumes as 1unit.
Use option to Slove this
1.we know that x's 1day work= 1/20.
Same y's=1/12
Choose option no. a, i.e .6 if x work for 6 days so y work for 2 days because y start working after 4 days so.
6/20+2/12 = 1,
Is not equal to 1.
So, the answer is not 6.
Take another i.e.10.
If x takes 10 days, y takes 6 days.
10/20+6/12 = 1.
Lhs=rhs . So the ans. Is 10days.
Lakshit said:
7 years ago
@Shweta.
Can you please elaborate last line?
Can you please elaborate last line?
Ajay said:
8 years ago
x+4/20+x/12 = 1.
3(x+4)+5(x)/60 = 1.
3x+12+5x = 60.
8x+12 = 60.
8x = 60-12.
8x = 48.
x = 6.
i.e., x+4 = 6+4.
10 days.
3(x+4)+5(x)/60 = 1.
3x+12+5x = 60.
8x+12 = 60.
8x = 60-12.
8x = 48.
x = 6.
i.e., x+4 = 6+4.
10 days.
Prudhvi said:
8 years ago
(4/20)+x(1/20+1/12) = 1,
Solve for x.
x=6.
Total days = x+4.
Solve for x.
x=6.
Total days = x+4.
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