A and B can finish a piece of work in 12 days and 15 days respectively. Together they start the work but after few days B left the job. After how many days had B left the job if A finished the remaining work in 3 days?

05

Total work = efficiency × number of days

Work done by A in 3 days = 3 × 5 = 15R

Remaining work = 60R - 15R = 45R

Total efficiency = 5R + 4R = 9R

Time taken when A & B worked together  = \(\frac{45R}{9R}\) = 5 days