Here we are considering work as 1 unit of work.

X --- does 1 unit of work in 4 hours => rate of x = 1/4

Y ---- does 1 unit of work in 8 hours =>rate of y = 1/8

together

their rate is 1/4+1/8 = 3/8

work - same 1 unit of work = 1

time it will take do the unit work = 1/(3/8) = 8/3 hours

Hope its clear now.

aks1985 wrote:

subhashghosh wrote:

Yes, your answer is correct.

Btw, 240 files information is irrelevant here, as both do the same work, it can be regarded as 1 unit of work.

In 1 hr, both finish = 1/8 + 1/4 = (1+2)/8 part of work

So total in 8/3 hrs

= 2 2/3 hrs

= 2 hrs 40 min

I like this approach. But can someone tell me why 3/8 was flipped to 8/3 to get the final answer?