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(7)\x05Byusingthedigits0,1,2,3,4and5Johnarrangesthenumberinascendingorderasfollow:\x050,1,2,3,4,5,10,11,12,13,14,15,20,21,22,23,24,25,30,31,….\x05(a)\x05Howmanyofthe10-digitnumbershaveexactlythree4s?[4marks]\x05(b)\x05What
题目详情
(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?
\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?
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答案和解析
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
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
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