Aptitude - Time and Work - Discussion

A's total work = 1.
A's 1 day work = 1/20 = 0.05.
B's 1 day work = 1/30 = 0.03.
c's 1 day work = 1/60 = 0.01.

B + C combined work together = 0.03 + 0.01 = 0.04.
A's 3 day work = 0.05 + 0.05 + 0.05 + 0.04 = 0.19.
If answer is 15 means = 5 * (0.19) = 0.95 remaining 0.05.

So, the answer is wrong.
In 16th day = (15days work + A's one day work).
= (0.95 + 0.05),
= 1.

So, 16 days is the correct answer.

I am not understanding A's 2 day's work. Please explain.

@All.

Please explain the last step.

Here, first of all, we have to find the total work.
So for this, L.C.M of 20 30 60 = 60,
a's b's c's one day work =3 2 1 (one day work)
Now a's 2days work = 6.
b's, c,s one day's woks = 2.
+1= 3.
So three days work 3 + 3 + 3 + 3 = 12.
3 days = 12
3*5 =15 days, 12 * 5 = 60.

I'm finding difficulty in understanding the question. How to analyze the question? Please help me out.

Why here they take 2?

Here first we take LCM of 20,30,60 that is 60.
After that , A work done = 60/20 = 3
Similar, B =60/30 = 2 and C = 60/60 = 1.

According to questions, A is assisted by B and C on every 3rd day.
i.e : 3 persons are Working.

Total work = A + A +(A + B + C) (Here a ,B and come together on every third day).
Total work = 3 + 3 + (3 + 2 + 1) = 12.

Now work = 60 is divided by 12 rem is 0.
Means 60/12 = 5 . We got 5 and 3 persons are working.
So that, 5 *3 = 15 days.

How did we get that 1/10+1/10 ? Can anyone help me?

Here A's 2 days work = 1/20 * 2 = 1/10,
And every third day A, B and C working together,
Means A, B, C's 1 day work is A + B + C = 1/20 + 1/30 + 1/60 = 3 + 2 + 1/60 = 6/60 = 1/10
So here complete 3 days work is 1/10 + 1/10 = 2/10 =1/5.
It means 1/5 work done in 3 days.
So work remains is 1 - 1/5 = 4/5.

So here,
1/5 : 4/5 :: 3 : x
1/5 * x = 4/5 * 3
x =12.

It means 4/5 work done in 12 days,
so complete work done in,
12 + 3 = 15days.

Therefore, the answer in 15.

Suppose B and C are helping a, = b 1/30 + c 1/60 + a 1/20.

But B and C are helping only on third day so( b+c / 3)+a = (1/30+1/60 =3/60 = 1/20/3=1/60)+ 1/20= 1/20+1/60=4/60=1/15 = 15.