AMC10 2018 B

Answer (D): The list has $2018-10=2008$ entries that are not equal to the mode. Because the mode is unique, each of these 2008 entries can occur at most 9 times. There must be at least $\left\lceil\frac{2008}{9}\right\rceil=224$ distinct values in the list that are different from the mode, because if there were fewer than this many such values, then the size of the list would be at most $9\cdot\left(\left\lceil\frac{2008}{9}\right\rceil-1\right)+10=2017<2018$. (The ceiling function notation $\lceil x\rceil$ represents the least integer greater than or equal to $x$.) Therefore the least possible number of distinct values that can occur in the list is 225. One list satisfying the conditions of the problem contains 9 instances of each of the numbers 1 through 223, 10 instances of the number 224, and one instance of 225.