+379 There are 9000 four-digit numbers, from 1000 to 9999, inclusive. Rather than counting the numbers with repeated digits, we'll count the numbers without a repeated digit. In this case, there are 9 choices for the first digit (all except 0), 9 choices for the second digit (all except the first), 8 choices for the third digit (two are already picked), and 7 choices for the fourth digit (three are already picked). Therefore, there are 9*9*8*7 numbers without a repeated digit, leaving 9000 - 9*9*8*7 numbers with a repeated digit. To find the percent, we divide this result by 9000, so we get
\(\frac{9000-9\cdot9\cdot8\cdot7}{9000}=\frac{1000-504}{1000}=.496\)
So, 49.6%
