1.常用百分数化分数
50% = 1/2 , 33% = 1/3 , 20% = 1/5, 10% = 1/10;

2.百分数整数部分（7-12）和分母的和为20
12.5% = 1/8 , 11.1% = 1/9 , 8.3% = 1/12, 7.7% = 1/13

3.（16，6）和(14,7)两对互换
16.7% = 1/6 , 6.25% = 1/16, 14.3% = 1/7 , 7.1% = 1/14

4.(17, 18, 19),5.963
5.9% = 1/17, 5.6% = 1/18, 5.3% = 1/19

5.6.7% = 1/15

百化分知识点常用于 已知：现期，增长率，计算增长量
计算步骤：
1.|r|=1/N,
2.增长量=现期/(N+1),减少量=现期/(N-1)