Answer : 4. "60/11"
Explanation :

Answer: D) 60/11 Explanation: A can complete the work in 12 days working 8 hours a day => Number of hours A can complete the work = 12×8 = 96 hours  => Work done by A in 1 hour = 1/96   B can complete the work in 8 days working 10 hours a day => Number of hours B can complete the work = 8×10 = 80 hours  => Work done by B in 1 hour = 1/80   Work done by A and B in 1 hour = 1/96 + 1/80 = 11/480  => A and B can complete the work in 480/11 hours   A and B works 8 hours a day. Hence total days to complete the work with A and B working together  = (480/11)/ (8) = 60/11 days