2020 AMC 10B Problem 22

Attempt Problem 22 of the 2020 AMC 10B 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 2020 AMC 10B solutions, or check the answer key.

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22.

What is the remainder when 2202+2022^{202} +202 is divided by 2101+251+1?2^{101}+2^{51}+1?

100100

101101

200200

201201

202202

Answer: D
Concepts:difference of squaresmodular arithmetic
Difficulty rating: 1880
Video solution:
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Written solution:

Let m=2101+251+1.m=2^{101}+2^{51}+1. We factor the numerator around this divisor: 2202+202=(2101+1)2(251)2+201. \begin{aligned} &2^{202}+202 \\ &\quad =(2^{101}+1)^2-(2^{51})^2+201. \end{aligned} By the difference of squares, (2101+1)2(251)2=(2101+251+1)(2101251+1), \begin{aligned} &(2^{101}+1)^2-(2^{51})^2 \\ &\quad =(2^{101}+2^{51}+1) \\ &\quad {}\cdot(2^{101}-2^{51}+1), \end{aligned} which is a multiple of m.m. Therefore 2202+202201(modm).2^{202}+202\equiv 201\pmod m.

Thus, the correct answer is D .

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