X and Y together can finish a work in 15 days. They worked on it for 10 days and then Y left. The remaining work was done by X alone in 15 days. In how many days can X alone finish the work?
45 days
Together (X+Y) did 10 × 115 = 23 rd of the work
Rest of the work 13 was done in 15 days. Hence X’s complete time = 3 ×15 = 45 days