Question

A can do a piece of work in 7 days of 9 hours each and b alone can do it in 6 days of 7 hours each. how long will they take to do it working together 42/5 hours a day?

Answer 1

A can do in 7 days by 9 hours a day

i.e. 9 × 7 = 63 hours

B can do in 6 days by 7 hours a day

i.e. 7 × 6 = 42 hours

A's work of 1 hour = 1/63

B's work of 1 hour = 1/42


together their work = 1/63 + 1/42

= 105 / 63 ×42

= 5/ 126 work per hour

so together they take 126 /5 hours to complete the work


so 126 / 5 = 3 × ( 42 /5 )

= 3 × ( 1 ) days ---- ( 42/5 hours means one day )

= 3 days