X can do a piece of work in 24 days. When he had worked for 4 days, Y joined him. If complete work was finished in 14 days, Y alone can finish that work in: MCQ with Answer and Explanation

Let total work be 24 units. Efficiency of X = 1 unit/day. X worked for all 14 days, so work done by X = 14 * 1 = 14 units. Remaining work = 24 - 14 = 10 units. This 10 units of work was done by Y. Y worked for 14 - 4 = 10 days. So Y's efficiency = 10 / 10 = 1 unit/day. Time taken by Y alone = 24 / 1 = 24 days.