Question

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

Answer 1

1.6 hr after initial two hour

A is first B is second

A in 6 hour = w

A in 1 hour = w/6

B in 4 hour = w

B in 1 hr = w/4

A & B together in 1 hr

= w/6 + w/4

= 5w/12

a worked in 2 hrs = 2*w/6

= w/3

workk left to do = w-w/3

= 2w/3

5w/12 is done in 1 hr

1 is done in 1/(5w/12)

2w/3 is done in (12/5w)*(2w/3)

= 8/5 hr

= 1.6 hr

Answer 2

If two men work with speed 6hrs and 4hrs respectively
then,if 1st man works for 2hrs and then accompanied by second
then,6-2=4