Aptitude - Time and Work - Discussion

@Sassy.

First, we have to calculate the work done for 1 day. For that we have to divide the number of days by 1.

So, A's 1 day work = 1/15 and B's 1 day work = 1/20.

Work done by A and B for 1 day is (1/15)+(1/20) = 7/60.

Here, L.C.M is taken.

As per question given, For 4 days, multiple with 4 then we can get.

Work done by A and B for 4 days = 4(7/60) = 7/15.

Here too L.C.M is taken.

Total work is 1(Assumption).

So,Work left = Total work - Work done by A and B.

Therefore, work left = 1-(7/15) = 8/15.

This is the answer.

I hope this helps you.

a = 15, b = 20, together c = 4 but LCM of in this 3 numbers is 60.

So a is 15(4), b is 20(3) and c is 4(15).

The first of 2 function is (4+3) remaining c(15).

The total of LCM(60).

15-7 = 8.

8/60 answer.

Why they take like this 1-(7/15)?

Let's total total work is 1.

A can do in 15 days.
A can do it in 1 days = 1/15.

Similarly B can do it = 1/20.
They work totally in a day = 1/15+1/20 = 7/60.

A and B do together in 4 days.
So work done in 4 days = 7/60x4 = 7/15.

Then left work is, Total work - 4 days work. i.e, 1-7/15 = 8/7 (Ans).

Can you explain how 7/60 came? AND Next steps.

Can you just guide me to know that how can we calculate the LCM of says 8, 24, 60/7.

@KARTHIKEYAN and @RAHUL.

DONT CONFUSE.

A can do in 15 days.
A can do it in 1 days = 1/15.

Similarly B can do it = 1/20.
They work totally in a day.

1/15+1/20 = 35/300 = 7/60.

Work done by A and B for 4 days = 4(7/60) = 7/15.

So, Work left = Total work - Work done by A and B.
Therefore, work left = 1-(7/15) = 8/15.

This is the answer.

I hope this helps you.

I take LCM for a and b 15, 20 = 60. Now I take per day work a and b.

a = 15*4 and b = 20*3.

So both together work 60/7.

Then I less 4 day work 4*7 = 28. So 60-28 = 32.

Therefore 32/7 or 4.567. This is right or wrong please explain.

7/60 = 20+15/300. But I am not understanding last step.

@Prem.

Always remember that while solving percentage total is 100% and similarly in ratio the total is 1/1 i.e 1.

Example : You can say that total work is done only when ratio comes in form of 1/1 , 2,2, 3,3,...... 50/50 and so on......

Answer will always come in 1/1(i.e total).