Aptitude - Time and Work - Discussion

Why we add 1/10 and 1/10 here? Please explain.

Nice explanation @Nikita.

How 6/60 come?

According to me, the answer is 12.

Simple, 3rd day B and C will hep A.
So first 2 days A will be working his work for two days is 2*(1/20) = 1/10.
Now 3rd day he is helped by B and C .
So A's work + B's work + C's work for 1 day is( 1/20 +1/30 +1/60) take LCM and solve we get 1/10.

Now A's 2days of work + (A+B+C's )work for 1 day.
1/10 +1/10 = 1/5.

So 1/5 work is completed which includes A's 2 days of work and Band C assistance for A (previous step same thing)
now
1/5 work is done in --- 3days
1( indicates complete work ) in ---- ? days

Ans is 15 days.

Nice explanation, Thanks @Vijay.

We have A work 2 days alone third-day B&C are added that means A+A+ (A+B+C) THIS is 3days work.

So A can do 2days work=1/10, and A+B+C 1day work=1/10, so add 1/10+1/10=1/5then total day work by A is 3*5=15.

Nice explanation, Thanks.

Simply;

A's 3 days works ----- 3/20.
B and C join on 3rd day so;
(A+B+C)'s 3 days work will be ---- 3/20 +1/30+ 1/60 = 12/60 = 1/5.
3 days work -- 1/5 then;
1 day work -- 1/15 part of 1 work (i.e 1/15 work in 1 days),
15 days = 1 work.

Take LCM ot 20,30 and 60 you will get total units of work i.e 360 units.
Now find the 1 day work by using UNITS/DAYS.
A=18 units
B=12 units
C=6 units
Now A+B+C 1 day work is 18+12+6=36 units.
A+B+C will complete the work in 10 days(360/36).

Now, B and C joins every 3rd day which means A will work for 2 days alone and A+B+C will work on the 3rd day.

A 1day work = 18,
A 2 day work= 18*2=36 units,
A+B+C 1 day work is 36 units,
So 3 days of work =36+36= 72 units,
So 1-day work will be 72/3.

Now total work was 360 units.
Total days= 360*3/72 = 15 Days.