Aptitude - Time and Work - Discussion

Here, A alone complete the whole work then answer is 20. Because total work is 60 and A's efficiency is 3.

Then 60/3 = 20 days.

For the peopel who are confused with last step.

We knew that 3 days work is 1/5.. the remaining work is 1-1/5=4/5.. ie already worked 3 days here.

Then we are calculating that how many 3 days are required to complete the remaining work 4/5.

Ie 4/5/1/5 = 4/5 * 5/1 = 4.. 4 (three days required).
ie 4*3 = 12 we already worked 3 days then total days will be 12 + 3 = 15.

Worker - TotalDay - OneDay
A - 20 - 1/20
B - 30 - 1/30
C - 60 - 1/60

1st Day - A.
2nd Day- B.
3rd Day - A, B, C.

They said A lonely can work for 2 day.
2A = 2(1/20) =1/10.

Then in third day A, B, C together;
(A+B+C) = 1/20+1/30+1/60,
= 1/10.

3 Days(not 3rd Day) work is;
=2A + (A+B+C).
= 1/10+1/10.
3Days =1/5 work,
6Days =2/5 work,
9Days =3/5 work,
12Days=4/5 work,
15Days= 5/5 =1 work completed.

Answer Explained:

A is working alone for two days, 3rd day he is assisted by B and C.

A's 1 day work=1/20
A working on 2 days=2*1/20=1/10

A+B+C working on 3rd day, so 1 day of working together=1/20+1/30+1/60=6/60=1/10

So total work done till 3rd day=1/10+1/10=2/10=1/5
So if in 3 days = 1/5 of work is completed....
Than, 3*5 days = 1/5*5 work will be completed.
=15days

Solution:

A do a piece of work in = 1/20 days.
'A' work alone for 2 days, so the work done by A on the second day is = 2/20 = 1/10
On the third day, A is assisted by B&C, then the work done by three of them is = 1/10 + 1/20 + 1/30 = 3/20.

Total work done by A in 3 days is = 1/20 + 3/20 = 1/5.

As we have to find number of days, so,

1/5 part of work done by A is in = 3 days.
1 part of the work done by A is in = 3x5 = 15 days.

In 15 days, A can do the work if he is assisted by B& C on the third day.

A's 2 day's work = (1/20x2) = 1/10.

(A + B + C)'s 1 day's work = [(1/20)+(1/30)+(1/60)] = 6/60 = 1/10.

Work done in 3 days = [(1/10)+(1/10)] = 1/5.

Now what they ask "How many days can "A" do the work?"

Here revise the FORMULA NO:2.

That is:

Days from Work:

If A's 1 day's work =1/n,then A can finish the work in n days.

Here ===> [1 DAY's work = NO.of WORK / required "n" Day's do the work ].

We want no.of DAY's;

So rearrange the formula; we get,

No.of WORK = (1DAY's work * "n" DAY's) ------> take eqn no.1.

Now, (1/5) work is done in 3 days.

3 = 1/5.

So apply above the data's in eqn no.1.

1(No.of Work) = (Day's of Work )3 * ("n" DAY's)5.

1(No.of Work) = 15 Day's

So "A" is require 15 Day's to do a 1 work.

"I HOPE U WILL B UNDERSTAND"

@Dhanam.

Because on third day they are doing combined work it means that for 1st 2 days they have worked alone here in question. About A has asked so he is doing only A.

Thanks all for explaining the answer.

How do you know total working day is 3 (last step).

3 days work = 1/5
it means 1 day work =1/15
that is 1/15 work is done in 1 Day
now 4/5 part of work that is (1-1/5) will be done in :15*4/5 =12 days....
Hence total work done will done in (12 + 3 ) days...