posted by Anna on .
The serial number on a $10 bill contains eight non-zero digits. If you $10 bill contains the digit 7 at least once, you win a prize. The probability that your $10 bill will be a prize-winning bill is?
Without a zero, there must be 9^8 number of possible digits. Further there must be 8^8 possible digits that exclude both zero and 7. So, the probability at at least one seven appears is 1.-((8^8)/(9^8))