解: 1/5 < a / b < 1 / 4 a和b都是自然数,由上式得: 1/5 < a / b b < 5a a / b < 1/4 4a < b a + b = 17 b=17 - a 分别 带入上式 即 4a < 17 - a 5a < 17 a < 17 / 5 17 - a < 5a 17 < 6a 17 / 6 < a 17 / 6 < a < 17 / 5 所以 a = 3 b = 17 - a = 17 - 3 = 14 故有:a = 3, b = 14 .
a是14:b是3