Question

ram and shyam can together paint a wall in 25 mins.ram can also paint the same wall in 50 mins. they work together for 20mins,then ram goes away.in how many mins will shyam paint the remaining part of the wall

Answer 1

In this question,
Both can paint the wall in 25 min.
They work together for 20 min , so
Part of wall painted = 20/25 = 4/5 .
Remaining part = 1-4/5 = 1/5.
Now, Ram can paint alone in 50 mins.
So, Shyam alone will paint in
(1/25 -1/50) = 1/50 part in 1 min.
then ,by Unitary method,
Shyam can paint 1/50 part in 1day.
So, 1/5 part will be in 1/(1/50)*(1/5) =10 min.

Hope it will help....
If any doubt, please ask.

Answer 2

ans is 10 mins.
-work done by ram in 1 min=1/50
work done in 1 min of both work together=1/25
now work done by both in 20 mins= 20×(1/25)
= 4/5
now part of work that can be done by shyam in 1 min = (1/25) - (1/50).
that is, work done by both in 1 min - work done by ram in 1 min
=1/50
work that is remaining to be done= 1 - (4/5)
= 1/5
now shyam can do this remaining work in,
=(1/5)÷(1/50)=10 mins
however the total time taken is (10 + 20) min
= 30mins