Aptitude - Time and Work - Discussion

Thanks for explaining @Swetha.

Thank for the explanation @Vikash.

How 7/60 came? Please explain me to get it.

A can complete work in 15 days.
B can complete work in 20 days.

total work (in units) = L.C.M of 15 and 20 => 60 units.

Unit work of A = Total work (in units)/Number of days A take to complete work => 60/15 = 4.

Unit work of B = Total work (in units)/Number of days B take to complete work => 60/20 = 3.

Work done in 1 day by A and B together = Unit work done by A + Unit work done by B => 4+3 = 7.

Work done by A and B together in 4 days = Work done by A and B together in 1 day * 4 => 7 * 4=28.

Work left = Total unit of work - work done by A and B together in 4 days => 60 - 28 = 32.

@Pooja

(1/15)+(1/20).
[(20+15)/(15*20)],
= 35/300,
= 7/60.

We know A done his work in 15 days and B in 20 days so total work is we take as 1.work is inversely proportion to days 1÷15 +1÷20=(15+20)/15x20=35/300=7/60=7x4/60=28/60=1-28/60=8/15.

Here 1 indicates total work.

By considering LCM 60 in that case why should we need to do remaining work divided by total work.

A' work is (1÷15) in one day,
B's work is (1÷20) in one day,

If both perform the work together then (1÷15)+(1÷20)=(35÷300) work is done in one day.
Now multiplying it by 4 so we get the amount of work done in 4 days.

(35÷300)*4 = (7÷15).
Now we know the total amount of work is 1.

Then subtract (1)-(7÷15)=(8÷15) the remaining work.

A=1/15 and b=1/20 ,a+b=7/60*4 =7/15 so,
1-7/15 = 8/15.

Can you explain why you have put 1_7/15?