Question 75890
Your question is a bit ambiguous, can I use each of those digits once, or as many times as I like?

If I can only use each digit once, then there are 5 choices for the first digit(1,2,3,4,5), 5, for the second(0,the four that are left), 4 for the third(we've used two), and 3 for the fourth, making 5*5*4*3=300.

If I can use each digit as many times as I like then there are 5 choices for the first digit and 6 choices for the second, third, and fourth digit, making 5*6*6*6=1080. Interestingly, you can work this out another way. If you think about it, an integer, x, is the number of non-negaitive integers strictly less than it, eg below five there are five non-negative integers 0,1,2,3,4. We are only interested in 4 digit numbers, and are working in base 6 so the answer is clearly *[tex (10000_6 - 1000_6)_{10}] Or going back to decimal, *[tex 6^4-6^3=6^3(6-1)=5.6^3]

Hope that helps,
Kev