A cricketer's average in his first 18 innings was 16.5 runs. After a further 8 innings, his average had increased to 32.5 runs. What was his average for the last 8 innings? Note: you don't need any cricket skills to solve this puzzle, nor do you need to know what an innings consists of.
His average was 68.5 runs. After the initial 18 innings, the average was 16.5, giving a total of 18 * 16.5 = 297 runs. There were 26 innings in total, with an average of 32.5 runs. Therefore an overall total of 26 * 32.5 = 845 runs. Therefore 845 - 297 = 548 runs were run in the final 8 innings, giving an average of 548 / 8 = 68.5 runs.