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:
355 comments Page 20 of 36.
Ashwini G C said:
1 decade ago
Hi friends,
Happy to see you all discussing the problems and the solution given by each of them is awesome.
In fact, I could solve the problem by seeing this 'discussion forum'. I had all the doubts as others had and I used to get a solution for it. So, I thought of thanking you all.
Happy to see you all discussing the problems and the solution given by each of them is awesome.
In fact, I could solve the problem by seeing this 'discussion forum'. I had all the doubts as others had and I used to get a solution for it. So, I thought of thanking you all.
Rasim shaikh said:
1 decade ago
Hello, friends!
Can anybody tell, how 1-7/15 get a plus? and I can't understand where the 1 come?
Please help me.
Can anybody tell, how 1-7/15 get a plus? and I can't understand where the 1 come?
Please help me.
Deepa said:
1 decade ago
@Swetha.
Thanks! Your explanation is very good and it is easy to understand.
Thanks! Your explanation is very good and it is easy to understand.
Harry said:
1 decade ago
I just came across an extremely easy way of solving this question. So felt like sharing it.
Work = LCM (15, 20) = 60 units.
A does 60/15 i.e. 4 units in a day, B does 60/20 i.e. 3 units in a day.
In 4 days work completed = (4 + 3) * 4 = 28 units.
Work left = Total work - work done by AB
= 60 - 28 = 32
So, Fraction of Work left = 32/60 = 8/15.
Work = LCM (15, 20) = 60 units.
A does 60/15 i.e. 4 units in a day, B does 60/20 i.e. 3 units in a day.
In 4 days work completed = (4 + 3) * 4 = 28 units.
Work left = Total work - work done by AB
= 60 - 28 = 32
So, Fraction of Work left = 32/60 = 8/15.
Deepa said:
1 decade ago
I'm confused with this stem (1 - 7/15). Can anyone explain this?
Arun said:
1 decade ago
Harry is correct.
Hi @Deepa, leave that 1-7/15 & %method, simply total efficiency is 7/day, no of worked together is 4, then multiply it becomes 28.
Subtract from total work done 60 - 28 = 32. To find the answer for ques-> 32/60 = 8/15. Cool.
Hi @Deepa, leave that 1-7/15 & %method, simply total efficiency is 7/day, no of worked together is 4, then multiply it becomes 28.
Subtract from total work done 60 - 28 = 32. To find the answer for ques-> 32/60 = 8/15. Cool.
Krishna said:
1 decade ago
I'm confused with this step (1 - 7/15). Can anyone explain this?
Pradosh behera said:
1 decade ago
Work is 1part. A and B work is finished 7/15 part in 4days from 1part. Remaining work is 1 - 7/15 = 8/15.
Meena said:
1 decade ago
Fraction of work done in 4 days = 7/15.
(It means that out of 15 parts, 7 parts has been done. So 8 parts left)
Therefore, the fraction of work left = 8/15.
(It means that out of 15 parts, 7 parts has been done. So 8 parts left)
Therefore, the fraction of work left = 8/15.
Santanu said:
1 decade ago
For those who have difficulty with fractions, here is an alternative.
Let the total work be to lay 120 bricks. (I chose 120 as it can be divided easily by both 15 and 20).
Takes 15 days to lay 120 bricks, That means in one day he can lay 8 bricks.
B takes 20 days to lay 120 bricks. That means B can lay only 6 bricks in one day.
Together they can lay 8+6=14 bricks.
Therefore, in 4 days, they will lay 14*4= 56 bricks only.
Remaining bricks to be layed is 120-56=64 bricks.
That means, 64/120=8/15 of the work is remaining.
Let the total work be to lay 120 bricks. (I chose 120 as it can be divided easily by both 15 and 20).
Takes 15 days to lay 120 bricks, That means in one day he can lay 8 bricks.
B takes 20 days to lay 120 bricks. That means B can lay only 6 bricks in one day.
Together they can lay 8+6=14 bricks.
Therefore, in 4 days, they will lay 14*4= 56 bricks only.
Remaining bricks to be layed is 120-56=64 bricks.
That means, 64/120=8/15 of the work is remaining.
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