Question

a can do a piece of work in 7 days of 9 hours ecah and b can do it in 6 days of 7 hours each. how long will they take to do it working together 8 2/5 hours a day?

Answer 1

For A: 7 days-9 hours daily-total 7*9= 63 hours of work
For B: 6 days-7 hours daily-total 6*7= 42 hours of work

Now work done by A in one hour =1/63
and work done by B in one hour =1/42

So, work done by A and B together in one hour =1/63 +1/42
=5/126
Now,
1 hour =5/126th part of the work
So time time taken for the whole work is 126/5hours

Therefore, total time taken by both A and B total complete the work =126/5

Now , work done daily by A and B =8 2/5 hours=42/5 hours (given)

So, total no. of days required =(126/5)÷(42/5)
=3 days

Therefore A and B together would take 3 days to complete the task