2017 AMC 10B Problem 16

Attempt Problem 16 of the 2017 AMC 10B below, then check your answer against the professionally curated solution from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2017 AMC 10B solutions, or check the answer key.

All problems are used with official legal permission of the Mathematical Association of America (MAA).

16.

How many of the base-ten numerals for the positive integers less than or equal to 20172017 contain the digit 0?0?
469469
471471
475475
478478
481481
Answer: A
Concepts:digitscomplementary counting
Small hint:
Count the complement: numbers with no digit 00
Big hint:
Split by one-, two-, three-, and four-digit numbers up to 20172017
Solution:
For numbers less than 100,100, we only have a 00 if it is a multiple of 10,10, of which there are 9.9.
For numbers between 100100 and 999999 inclusive, we will use complementary counting. There are 900900 total numbers in this range. Also, there are 9⋅9⋅9=7299\cdot 9\cdot 9=729 numbers in this range with no 00 since there are 99 ways to choose each digit to not be 0.0. Thus, the total in this range is 171.171.
For numbers between 10001000 and 19991999 inclusive, we will use complementary counting again. There are 10001000 total numbers in this range. Also, there are 1⋅9⋅9⋅9=7291\cdot 9\cdot 9\cdot 9=729 numbers in this range with no 00 since there are 99 ways to choose each of the last 33 digits to not be 00 and the first digit must be 1.1. Thus, the total in this range is 271.271.
There are 1818 numbers between 20002000 and 20172017 inclusive, each with a 00 in the second digit from the left.
This makes the total 9+171+271+18=469.9+171+271+18=469.
Thus, the correct answer is A .
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