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1. The problem statement, all variables and given/known data

Determine the sum of all the four digit numbers formed by using the digits 1,3,5, and 7. NO DIGIT REPEATED in any number.

2. Relevant equations

thats my question......

3. The attempt at a solution

I can solve this problem by simply writing out all of the terms and adding them up....

ie

1357+1375+...3157+3175+.....+ 5137+5173+...+7135+7153+...7531 =:zzz:

But is there a formla which I can use for these types of questions? For example if there were 9 different numbers I would not want to write out all the combinations and then add up all the numbers. It wasnt to difficult with just 4 but, I knowthere must be some formula or theorem out there.... Any ideas?

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# Is there a formula?

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