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.
Answers
Answer:
Let the first person be A and second person be B
A can complete the work in 6 hours
i.e For one hour, A completes one-sixth of total work
B can complete the work in 4 hours
i.e For one hour, B completes one-fourth of total work
Together they do five-twelfth of total work
i.e (1/6)+(1/4) = (4+6)/24 = 10/24 = 5/12
Case 1:
As A worked for two hours, he would complete one-third of the work.
The remaining work would be the two-third part
5/12 is the part of work which is completed together in an hour.
Divide 2/3 with 5/12
=> (2/3)/(5/12) = (2/3)*(12/5) = 24/15 = 8/5
So, the remaining part of the work is completed in 8/5 hours (1 hr 36 min)
The total work is completed in 18/5 hours (3 hrs 36 min)
Case 2
As B worked for two hours, he would complete half of the work.
The remaining work would be the half part
5/12 is the part of work which is completed together in an hour.
Divide 1/2 with 5/12
=> (1/2)/(5/12) = (1/2)*(12/5) = 12/10 = 6/5
So, the remaining part of the work is completed in 6/5 hours (1 hr 12 min)
The total work is completed in 16/5 hours (3 hrs 12 min)
Note: I had given two cases because the problem has not specified who is the first person.
Hope it helps