Time And Work

Step 1: Work Done by A.
A completes of the work in 15 days. The work done by A in 1 day is:

Step 2: Work Done by A and B Together.
The remaining work is . A and B together complete this work in 5 days, so their combined work rate is: Since A's work rate is , the work rate of B is:

Step 3: Time for A and B Together to Complete the Work.
The combined work rate of A and B is: The total time to complete the entire work is:

Final Answer: