(7)x05By using the digits 0,1,2,3,4 and 5 John arranges the number in ascending order as follow:

题目

(7)x05By using the digits 0,1,2,3,4 and 5 John arranges the number in ascending order as follow:
x050,1,2,3,4,5,10,11,12,13,14,15,20,21,22,23,24,25,30,31,….
x05(a)x05How many of the 10-digit numbers have exactly three 4s?
[4 marks]
x05(b)x05What is the number of the 99999th term?

答案

这样计数,其实就是个六进制的问题
a.10C3 = 10*9*8 / 3!= 120
b.只要把99999换成六进制就行了,如果你在学discrete math,那就应该会转换(不会的话再问我),答案是2050543