Question

Two men can do a piece of work in 6 hours and 4 hours respectively.After the first person has worked for 2 hours he is joined by other .By when should the work be completed

Answer 1

1st person can do 1 work in 6 hours
In 1 hour he does: 1/6 part of work
2nd person can do the same work in 4 hours
In 1 hour he does: 1/4 part of work.
1st person worked for 2 hours.
In 2 hours he did: 2*1/6 = 1/3 part of work
Work Remaining = 1 - 1/3 = 2/3 work

Now both the persons are working
In 1 hour both do: 1/6 + 1/4 = 2+3/12 = 5/12 work
1 hour== 5/12 work
X hours = 2/3 work
5X/12 = 2/3
X = 1.6 hours...
Hence the work will be completed in another 1.6 hours.
Hope it helps

Answer 2

Answer:

1st person can do 1 work in 6 hours

In 1 hour he does: 1/6 part of work

2nd person can do the same work in 4 hours

In 1 hour he does: 1/4 part of work.

1st person worked for 2 hours.

In 2 hours he did: 2*1/6 = 1/3 part of work

Work Remaining = 1 - 1/3 = 2/3 work

Now both the persons are working

In 1 hour both do: 1/6 + 1/4 = 2+3/12 = 5/12 work

1 hour== 5/12 work

X hours = 2/3 work

5X/12 = 2/3

X = 1.6 hours...

Hence the work will be completed in another 1.6 hours.

Hope it helps