Question 369915
Consider the complementary event of a 7 NOT appearing as a digit in the 8 digits.  We then have 8 choices for filling 8 spaces.  The probability that a 7 will not appear is then{{{8^8/9^8 = (8/9)^8}}}, and the probability of a 7 appearing at least once is {{{1-(8/9)^8 = 0.610255656}}}.  That is also the probability for a prize-winning bill.