Difference between revisions of "2023 AMC 12A Problems/Problem 3"
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− | All it takes is to recall that 45 squared is 2025, and 45 is 5 x 9. So all the squares of 5 x 1, 5 x 2, 5 x 3 so on are divisible by 5. So the answer is | + | All it takes is to recall that 45 squared is 2025, and 45 is 5 x 9. So all the squares of 5 x 1, 5 x 2, 5 x 3 so on are divisible by 5. So the answer is 8. It can be done even if one does not remember that 45 squared is 2025, all it takes is intuition. One can easily see mentally that 5 x 8 that is 40 squared is 1600, and then one has to do just one more computation and see that 5 x 9 that is 45 squared exceeds 2023, so the answer is 8. BlueShardow's method is the best but he did not realize it. |
~edit by RobinDaBank | ~edit by RobinDaBank |
Revision as of 01:18, 7 July 2024
- The following problem is from both the 2023 AMC 10A #3 and 2023 AMC 12A #3, so both problems redirect to this page.
Contents
[hide]- 1 Problem
- 2 Solution 2 (slightly refined)
- 3 Solution 3
- 4 Solution 4
- 5 Solution 5 (Under 10 seconds, ignore the first paragraph)
- 6 Video Solution (easy to understand) by Power Solve
- 7 Video Solution by Math-X (First understand the problem!!!)
- 8 Video Solution by CosineMethod [🔥Fast and Easy🔥]
- 9 Video Solution
- 10 Video Solution (🚀 Just 2 min 🚀)
- 11 Video Solution (easy to digest) by Power Solve
- 12 Video Solution (Easy to Understand) by DR.GOOGLE (YT: Pablo's Math)
- 13 See Also
Problem
How many positive perfect squares less than are divisible by ?
Solution 2 (slightly refined)
Since , there are perfect squares less than 2023.
~not_slay
Solution 3
Since is prime, each solution must be divisible by . We take and see that there are positive perfect squares no greater than .
~jwseph
Solution 4
~kyogrexu (minor edits by vadava_lx) ~ It was just a worse way of describing solution 5, hence removed by ~ Dextrik
Solution 5 (Under 10 seconds, ignore the first paragraph)
The original way of BlueShardow
Since the perfect squares have to be divisible by 5, then we know it has to be 5 times some number squared (5*x)^2. With this information, you can fique out every single product of 5 and another number squared to count how many perfect squares are divisible by 5 that are less than 2023. (EX: 5^2 = 25, 10^2 = 100, ... 40^2 = 1600) With this you get a max of 40^2, or solutions. PLEASE DO NOT do this problem this way, it takes way too much time.
~BlueShardow
The way of BlueShardow refined:
All it takes is to recall that 45 squared is 2025, and 45 is 5 x 9. So all the squares of 5 x 1, 5 x 2, 5 x 3 so on are divisible by 5. So the answer is 8. It can be done even if one does not remember that 45 squared is 2025, all it takes is intuition. One can easily see mentally that 5 x 8 that is 40 squared is 1600, and then one has to do just one more computation and see that 5 x 9 that is 45 squared exceeds 2023, so the answer is 8. BlueShardow's method is the best but he did not realize it.
~edit by RobinDaBank
Video Solution (easy to understand) by Power Solve
https://youtu.be/YXIH3UbLqK8?si=aIYHWEU82uUu21fQ&t=165
Video Solution by Math-X (First understand the problem!!!)
https://youtu.be/cMgngeSmFCY?si=E0a8wvcNRoeg2A3X&t=422
Video Solution by CosineMethod [🔥Fast and Easy🔥]
https://www.youtube.com/watch?v=wNH6O8D-7dY
Video Solution
~Steven Chen (Professor Chen Education Palace, www.professorchenedu.com)
Video Solution (🚀 Just 2 min 🚀)
~Education, the Study of Everything
Video Solution (easy to digest) by Power Solve
https://www.youtube.com/watch?v=8huvzWTtgaU
Video Solution (Easy to Understand) by DR.GOOGLE (YT: Pablo's Math)
See Also
2023 AMC 10A (Problems • Answer Key • Resources) | ||
Preceded by Problem 2 |
Followed by Problem 4 | |
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 |
2023 AMC 12A (Problems • Answer Key • Resources) | |
Preceded by Problem 2 |
Followed by Problem 4 |
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.