设有x只鸡,则有 12 - x 只兔子.
2x + 4(12 - x) = 38
2x + 48 - 4x = 38
4x - 2x = 48 - 38
2x = 10
x = 5
鸡 = x = 5
兔子 = 12 - x = 7
答：有5只鸡,有 7 只兔子.