permutation(urgent!!!)

There are altogether 5! =120 ways to arrange the digits
Consider for example, the unit digit, out of these 120 permutations,
24 have 1, 24 have 2, 24 have 3, 24 have 5 and 24 have 9 as unit digit.
Therefore sum of unit digit = 24*(1+2+3+5+9)=480
Likewise for the other digits, so the sum of all 120 numbers
=480*(1+10+100+1000+10000)
=5333280

2010-04-23 23:51:30 補充：
Each of the 5 digits have equal chance to appear in the 120 numbers. 120/5=24

2010-04-24 00:16:57 補充：
sum of unit digit = 24*(1+2+3+5+9)=480
sum of tens digit = 24*(10+20+30+50+90)=480*10
sum of hundreds digit = 24*(100+200+300+500+900)=480*100, etc
So ttl = 480*(1+10+100+1000+10000)=5333280

What is the sum of all the different five-digit integers formed by using the
digits 1，2，3，5，9 without repetition?
Sol
5!/5=24
1+2+3+5+9=20
20*11111*24=5333280