Difference between revisions of "2024 AMC 10B Problems/Problem 18"
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− | Notice that all the answer choices are multiples of <math>5</math> except for <math>1</math> and <math>2</math>. <math>2</math> doesn't seem to fit in with the other answer choices, so you can assume that it is the answer <math>\boxed{\textbf{(B)} 2}</math>. | + | Notice that all the answer choices are multiples of <math>5</math> except for <math>1</math> and <math>2</math>. <math>2</math> doesn't seem to fit in with the other answer choices, so you can assume that it is the answer: <math>\boxed{\textbf{(B)} 2}</math>. |
Written by ChristianZhang | Written by ChristianZhang |
Revision as of 14:06, 15 November 2024
- The following problem is from both the 2024 AMC 10B #18 and 2024 AMC 12B #14, so both problems redirect to this page.
Contents
[hide]Problem
How many different remainders can result when the th power of an integer is divided by ?
Solution 1
First note that the Euler's totient function of is . We can set up two cases, which depend on whether a number is relatively prime to .
If is relatively prime to , then because of Euler's Totient Theorem.
If is not relatively prime to , it must be have a factor of . Express as , where is some integer. Then .
Therefore, can only be congruent to or . Our answer is .
~lprado ~edit by Elephant200
Solution 2 (Euler Totient)
We split the cases into:
1. If x is not a multiple of 5: we get
2. If x is a multiple of 125: Clearly the only remainder provides 0
Therefore, the remainders can only be 1 and 0, which gives the answer .
~mitsuihisashi14
Solution 3 (No Totient)
Note that
Taking this mod , we can ignore most of the terms except the for the last :
so . Substituting for , we get . Therefore, the remainders when divided by repeat every integers, so we only need to check the th powers of . But we have that and , so we really only need to check . We know that produce different remainders, so the answer to the problem is either or . But is not an answer choice, so the answer is .
Solution 4 (Totient)
Euler's Totient Function, returns as a product of each prime divisor of .
Euler's Totient Theorem states that if is an integer and is a positive integer relatively prime to , then .
In this case, , which is convenient because only has one prime factor, , therefore , so where . Every single number that isn't a multiple of is relatively prime to , therefore we have two cases:
1)
2)
The answer is ~Tacos_are_yummy_1
Solution 5 (Binomial Theorem)
~Kathan
Solution 7 (Guess)
Notice that all the answer choices are multiples of except for and . doesn't seem to fit in with the other answer choices, so you can assume that it is the answer: .
Written by ChristianZhang
Video Solution 1 by Pi Academy (Fast and Easy ⚡🚀)
https://youtu.be/c6nhclB5V1w?feature=shared
~ Pi Academy
Video Solution 2 (Fast!)
https://www.youtube.com/watch?v=S7l_Yv2Sd7E
See also
2024 AMC 10B (Problems • Answer Key • Resources) | ||
Preceded by Problem 17 |
Followed by Problem 19 | |
1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 • 19 • 20 • 21 • 22 • 23 • 24 • 25 | ||
All AMC 10 Problems and Solutions |
2024 AMC 12B (Problems • Answer Key • Resources) | |
Preceded by Problem 13 |
Followed by Problem 15 |
1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 • 19 • 20 • 21 • 22 • 23 • 24 • 25 | |
All AMC 12 Problems and Solutions |
The problems on this page are copyrighted by the Mathematical Association of America's American Mathematics Competitions.