No math required. Almost. When we have multiple options for a series of decisions, we can multiply the number of options for each decision. In this case, the first two decisions are which letter to choose, and the last three decisions are which digit to choose. Since there are 26 letters, and 10 digits, and repetition is allowed, we can multiply as follows:

26x26x10x10x10 = ?

Advanced math students should know what 26 squared is, but we don't need to actually multiply these numbers to solve this problem. Whatever the number is, it must end in 3 zeros. Notice only one answer choice does so: E.
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