A does 20% less work than B. if A can complete a piece of work in 7 ½ hours, then B can do it in

6 hours

B can finish the work in 80% of 7 ½ hours of time

7 ½ = 15/2

Therefore, time taken by B = .8 × 15/2 = 30/5 = 6 hours.

let B=100% then A=80%{since A does 20% less work than B} A:B=80:100

A:B=4:5, let B can complete the work in p hours .

So, 4:5=15/2:p

4/5=15/2p

P=6

B can do it in 6 hours.