我们在生活中可以体会到,钞票的面额最多的就是1、2、5、10这4种,要么就是它们的10倍数。为什么没有3块钱的钞票呢?货币面值是依据数学的组合原理来设计的。在1到10里,有重要数和非重要数之分,1、2、5、10就是重要数,用这几个数能以最少的加减运算得到另外一些数,例如:1+2=3,1+5=6,10-2=8,10-1=9。而从概率学的角度看:在1至9的各种数字排列组合中,3 We can understand in our life that the largest denomination of banknotes is 1, 2, 5 and 10, or 10 times of them. Why there is no 3 dollar bill? The currency denomination is based on the principle of mathematical combination to design. In 1 to 10, there are important and non-important number of points, 1, 2, 5, 10 is the important number, with these few can be the least addition and subtraction operation to get some other numbers, for example: 1 +2 = 3, 1 + 5 = 6, 10-2 = 8, 10-1 = 9. From a probabilistic point of view: in the various combinations of numbers from 1 to 9, 3