The best way to solve this problem is to think backwards. Since the eldest daughter got the "half" and "half" of the last remaining cow, she didn't kill 1, so there was nothing left, so she had to get 1. Second son: The eldest daughter gets half as many cows as the second son, so the second son gets twice as many cows as the eldest daughter: two cows. Eldest son: The second son gets half as many cows as the eldest son, so the eldest son gets twice as many cows as the second son: four cows. Wife: The eldest son gets half as many cows as the wife, so the wife gets twice as many cows as the eldest son: eight cows. The number of cows obtained by four people adds up: 1+2+4+8= 15. It can be seen that the number of cows left by farmers is 15.