Aptitude - Time and Work - Discussion

How 7/60 come?

How to solve 1/15 + 1/20? Explain me.

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.

Hello, friends!

Can anybody tell, how 1-7/15 get a plus? and I can't understand where the 1 come?

Please help me.

@Swetha.

Thanks! Your explanation is very good and it is easy to understand.

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.

I'm confused with this stem (1 - 7/15). Can anyone explain this?

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.

I'm confused with this step (1 - 7/15). Can anyone explain this?

Work is 1part. A and B work is finished 7/15 part in 4days from 1part. Remaining work is 1 - 7/15 = 8/15.

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.