2 men can do a peice of work in 6 hours and 4 hours respectively. After the first has worked for 2 hours' he is joined by the other. By when should the work be compleated?
Let two men are A and B.
Given: A can do a piece of work in 6 hours and B can do in 4 hours. Thus,
A’s 1 hour work = 1/6
And, B’s 1 hour work = 1/4
And, (A+B)’s 1 hour work = 1/6 + 1/4 = 5/12
After the first has worked for 2 hours ' he is joined by the other, so,
(A)’s 2 hour work = 2(1/6) = 1/3
Remaining work = 1-1/3 = 2/3
Since, 5/12 work is done by (A+B) in 1 hrs
Therefore, 2/3 work is done by (A+B) in 12/5 × 2/3 = 8/5 hrs
Therefore,
Total time to be completed the work = 2 + 8/5 = 18/5 = 3 hrs.