Difference between revisions of "2021 AMC 12A Problems/Problem 14"
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==Video Solution by Hawk Math== | ==Video Solution by Hawk Math== | ||
https://www.youtube.com/watch?v=AjQARBvdZ20 | https://www.youtube.com/watch?v=AjQARBvdZ20 | ||
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| + | == Video Solution by pi_is_3.14 (Using Logarithmic Manipulations) == | ||
| + | https://youtu.be/vgFPZ-hyd-I | ||
==See also== | ==See also== | ||
{{AMC12 box|year=2021|ab=A|num-b=13|num-a=15}} | {{AMC12 box|year=2021|ab=A|num-b=13|num-a=15}} | ||
{{MAA Notice}} | {{MAA Notice}} | ||
Revision as of 18:33, 11 February 2021
Contents
Problem
What is the value of![\[\left(\sum_{k=1}^{20} \log_{5^k} 3^{k^2}\right)\cdot\left(\sum_{k=1}^{100} \log_{9^k} 25^k\right)?\]](http://latex.artofproblemsolving.com/9/9/3/9934e0771c30ad96de59aa26766c6befd3570ccd.png)
Solution
This equals
![\[\left(\sum_{k=1}^{20}k\log_5(3)\right)\left(\sum_{k=1}^{100}\log_9(25)\right)=\frac{20\cdot21}{2}\cdot\log_5(3)\cdot100\log_3(5)=\boxed{\textbf{(E)} 21000}\]](http://latex.artofproblemsolving.com/1/e/e/1ee3550086ed338d704398aad18c9252b730baea.png)
~JHawk0224
Video Solution by Punxsutawney Phil
https://youtube.com/watch?v=FD9BE7hpRvg&t=322s
Video Solution by Hawk Math
https://www.youtube.com/watch?v=AjQARBvdZ20
Video Solution by pi_is_3.14 (Using Logarithmic Manipulations)
See also
| 2021 AMC 12A (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 | |
These problems are copyrighted © by the Mathematical Association of America, as part of the American Mathematics Competitions. 
