Suppose A and B can complete a work together in 10 days. If B alone can complete the work in 15 days, then in how many days can A alone finish the work?

To solve work and time problems, individual work rates are calculated as the reciprocal of the time taken to complete the task. The combined work rate of multiple workers is the sum of their individual rates. In this problem, the combined rate of A and B is 1/10 job per day, and B's individual rate is 1/15 job per day. To find A's individual rate, subtract B's rate from the combined rate: 1/10 - 1/15. Using a common denominator of 30, this becomes 3/30 - 2/30 = 1/30 job per day. Since A completes 1/30 of the work in one day, the total time required for A to finish the work alone is the reciprocal of the rate, which is 30 days.