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标题: please help this stupid head! [打印本页]

作者: hollandgirl 时间: 2006-10-13 23:56
标题: please help this stupid head!

Q19:

How many 4-digit positive integers are there in which all 4 digits are even?

A. 625

B. 600

C. 500

D. 400

E. 256

my choice is A,but the answer given is C, I am confused.help me!

[此贴子已经被作者于2006-10-14 0:05:57编辑过]

作者: magileilei 时间: 2006-10-14 00:16

对的呀,千位数字可以是2,4,6,8 个/十/百位数可以是0,2,4,6,8

c(4,1)*c(5,1)*c(5,1)*c(5,1)=500

作者: hollandgirl 时间: 2006-10-14 01:26

谢谢！

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