设这个两位数十位是 x ,则个位是 x + 1
10x + x + 1 = 5(x + x + 1)
11x + 1 = 10x + 5
11x - 10x = 5 - 1
x = 4
十位 = x = 4
个位 = x + 1 = 5
所以这个两位数是 45