A can complete a piece of work in 40 days and B can complete the same work in 60 days. They work together for 8 days. How much work is left?

Correct option is C

Total Work = LCM of 40 and 60 = 120 unit

Efficiency of A  = $$\frac {120}{40}$$​ = 3 unit per day

Efficiency of B = $$\frac {120}{60} = 2$$​ unit per day

Work done by both of them in 8 days = (3+2)× 8 = 40 unit

Remaining Work left = 20-40 = 80

Work fraction left = $$\frac{80}{120}= \frac{2}{3}$$​​