please help this stupid head!

hollandgirl

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]

magileilei

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

hollandgirl

谢谢！