Difference between revisions of "2024 AMC 10A Problems/Problem 19"
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<math>\textbf{(A) } 9 \qquad \textbf{(B) } 12 \qquad \textbf{(C) } 16 \qquad \textbf{(D) } 18 \qquad \textbf{(E) } 21</math> | <math>\textbf{(A) } 9 \qquad \textbf{(B) } 12 \qquad \textbf{(C) } 16 \qquad \textbf{(D) } 18 \qquad \textbf{(E) } 21</math> | ||
==Solution== | ==Solution== | ||
| − | For a geometric sequence, we have <math>ab=720^2=2^8 3^4 5^2</math>, and we can test values for <math>b</math>. We find that <math>b=768</math> and <math>a=675</math> works, and we can test multiples of <math>5</math> in between the two values. Finding that none of the multiples of 5 divide <math>720^2</math> besides <math>720</math> itself, we know that the answer is <math>7+6+8=\boxed{\textbf{(E)}21</math>. | + | For a geometric sequence, we have <math>ab=720^2=2^8 3^4 5^2</math>, and we can test values for <math>b</math>. We find that <math>b=768</math> and <math>a=675</math> works, and we can test multiples of <math>5</math> in between the two values. Finding that none of the multiples of 5 divide <math>720^2</math> besides <math>720</math> itself, we know that the answer is <math>7+6+8=\boxed{\textbf{(E)}21}</math>. |
~eevee9406 | ~eevee9406 | ||
Revision as of 15:53, 8 November 2024
Problem
The first three terms of a geometric sequence are the integers 
and 
where 
What is the sum of the digits of the least possible value of 
Solution
For a geometric sequence, we have 
, and we can test values for 
. We find that 
and 
works, and we can test multiples of 
in between the two values. Finding that none of the multiples of 5 divide 
besides 
itself, we know that the answer is 
.
~eevee9406
