Difference between revisions of "1974 AHSME Problems/Problem 8"

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==See Also==
 
==See Also==
 
{{AHSME box|year=1974|num-b=7|num-a=9}}
 
{{AHSME box|year=1974|num-b=7|num-a=9}}
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[[Category:Introductory Number Theory Problems]]
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{{MAA Notice}}

Latest revision as of 12:42, 5 July 2013

Problem

What is the smallest prime number dividing the sum $3^{11}+5^{13}$?

$\mathrm{(A)\ } 2 \qquad \mathrm{(B) \ }3 \qquad \mathrm{(C) \  } 5 \qquad \mathrm{(D) \  } 3^{11}+5^{13} \qquad \mathrm{(E) \  }\text{none of these}$

Solution

Since we want to find the smallest prime dividing the sum, we start with the smallest prime and move up, so first we try $2$. Notice that $3^{11}$ and $5^{13}$ are both odd, so their sum must be even. This means that $2$ must divide $3^{11}+5^{13}$, and so since $2$ is the smallest prime, our answer must be $2, \boxed{\text{A}}$.

See Also

1974 AHSME (ProblemsAnswer KeyResources)
Preceded by
Problem 7
Followed by
Problem 9
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 26 27 28 29 30
All AHSME Problems and Solutions

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