Working 5 hours a day, A can Complete a work in 8 days and working 6 hours a day, B can complete the same work in 10 days. Working 8 hours a day, they can jointly completely the work in?

4.5 days

4 days

3 days

None of these

1 hour's work of A = 2.5% (meaning A completes 2.5% of the work in 1 hour)

1 hour's work of B = 1.66% (meaning B completes 1.66% of the work in 1 hour)

Combined work rate of A and B in 1 hour = 2.5% + 1.66% = 4.16%

Time to complete the work = 100%/4.16% = 24 hours (since they work 8 hours a day, this is equivalent to 3 days)

So, A and B together can complete the work in 3 days, working 8 hours a day.