Solution: 100 fish 100 kg, of which one fish 1 kg. For example, if this fish is removed first, the remaining two kinds of fish are exactly x Jin (N+X= 100, 0 < x < 100). 16 fish a catty, because fish is an integer, 16 fish a catty bought 16 or 32 or 48 fish, in short, it is a multiple of 16, otherwise the calculated catty is not an integer. Look at the fish per catty 16. If you buy 16 fish, the number of fish is 15, and if you buy 32 fish, it is 15×2 = 30. In short, the number of fish you bought is a multiple of 65,438+05. On the other hand, there are 1 fish in five Jin, and the number of Jin is greater than the number of fish is a multiple of 4. The Jin of these two kinds of fish is the same as the number of fish, so the number of fish in 16 Jin should be exactly the same as that in 1 5 Jin. So this number is the common multiple of 15 and 4, the smallest common multiple is 60, the second smallest common multiple is 120, and the total number of fish is only 100, so this number is 60. 60 is four times that of 15, so a kilo of 16 fish is four times that of 16, and 60 is four times that of 15, so a kilo of 1 fish is 15.