2016 AMC 8 Problem 5

Attempt Problem 5 of the 2016 AMC 8 below, then check your answer against the video solution and professionally curated solution from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2016 AMC 8 solutions, or check the answer key.

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

5.

The number NN is a two-digit number with the following properties:
  • When NN is divided by 9,9, the remainder is 1.1.
  • When NN is divided by 10,10, the remainder is 3.3.
What is the remainder when NN is divided by 11?11?
0 0
2 2
4 4
5 5
7 7
Answer: E
Concepts:modular arithmeticsystematic listing
Small hint:
The remainder when divided by 1010 tells you the units digit of NN.
Big hint:
List the two-digit numbers ending in 33 and test the condition modulo 99.
Video solution:
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Written solution:
The second condition says that NN ends in 33, so the possibilities are 13,13, 23,23, 33,33, 43,43, 53,53, 63,63, 73,73, 83,83, 93.93. Of these, only 7373 leaves remainder 11 when divided by 99, because its digit sum is 1010. Finally, 73=6⋅11+773=6\cdot11+7, so the requested remainder is 77.
Thus, E is the correct answer.
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