Aptitude - Time and Work - Discussion

Can you explain how 7/60 came?

A+b 1 days work =7/60.

@Poorni:

The total work = 1;

Work done by A and B in 4 days = 7/15.

Therefore, the pending work = 1 - 7/15 = 0.533333333... (or) 8/15.

Hope this help you. Have a nice day!

@Deepa

(1/50+1/20) = (20+15)/300 //This get by cross multiplication.

= 35/300

= 7/60.

I think your doubt is clear now.

Why (1-7/15) is applied ?

@Beer Ibrahim

Q: Why (1-7/15) is applied ?

Ans: To calculate the work remaining. Work remaining = 8/15.

Note: From the above answer, we can say 15/8 days required to
complete the remaining work by A and B.

Hope this will help you. Have nice day!

For A:-
15 days for 1 job
in 1 day 1/15 (part of the one job)
for B:-
20 days for 1 job
in 1 day 1/20 (part of the one job)
FOR BOTH IN ONE DAY:-
1/15+1/20=7/60
FOR BOTH IN 4 DAYS:-
(7/60)*4=7/15(THEY HAVE DONE)
THE REST PART OF THE JOB IS:-
1-(7/15)=8/15 (ANS)

We can solve this problem by another way also..let us see..

A can do a work in 15 days
B can do a work in 20 days
Take LCM for 15 & 20 i.e Total work = 60

Then,
A's capacity = 60/15 = 4
B's capacity = 60/20 = 3
They work together for 4 days,

Then, A's capacity + B's capacity = 4 + 3 =7
AB's one day capacity = 7
since they work for 4 days, they have done 4x7 =28 work
Work left = Total work - work done by AB
= 60 - 28 = 32
Remaining work / total work = 32 / 60 = 8 / 15

This method will take less time to compute guys...please try it.

When dealing with addition or subtraction of fractions you consider the denominators i.e
15&20 and then you find the L.C.M which is 60 or multiply them together.

15*20 = 300 so,

(1/15 + 1/20)/300 = (20 + 15)/300.

=25/300 reduce to the lowest term and you get 7/60.

This 7/60 is the amount of work A & B will complete in one day.
Hence for 4 days we have;

7/60 * 4 = 7/15 of the total work.

Since we don't know the real value of the total work we then assume total work to be done to be 1.

Therefore,

Remaining work left will be,

1- (work done)

1-7/15 ; the denominator here is 15 & 1 (since 1 =1/1).

Do the math and you get our final answer to be 8/15.

NOTE !

If you are subtracting a fraction from a whole number, just multiply the denominator by the whole number and then subtract from the numerator. The same rule applies for addition.

Thanks all.