R1+R2 = 20
R1/B1 = 1/2,
所以 R1 = 1/2 * B1
R2/B2 = 3/5
所以 R2 = 3/5 *B2
R1 + R2 = 1/2 * B1 + 3/5 *B2 = 20
等式两边都乘以10, 5B1 + 6B2 = 200
B1 = (200 - 6B2)/5 = 40 - 6B2/5
能被5除尽的B2数字有: 5,10, 15, 20, 25,30
对应的B1是:34, 28, 22, 16, 10, 4
B1 + B2 = 34,35, 36, 37, 38, 39