Art of Problem Solving

1956 AHSME Problems/Problem 31: Difference between revisions

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== Problem 31==
In our number system the base is ten. If the base were changed to four you would count as follows:
<math>1,2,3,10,11,12,13,20,21,22,23,30,\ldots</math> The twentieth number would be:
<math>\textbf{(A)}\ 20 \qquad\textbf{(B)}\ 38 \qquad\textbf{(C)}\ 44 \qquad\textbf{(D)}\ 104 \qquad\textbf{(E)}\ 110 </math>
==Solution==
==Solution==


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~JustinLee2017
~JustinLee2017
==See Also==
{{AHSME 50p box|year=1956|num-b=30|num-a=32}}
{{MAA Notice}}

Latest revision as of 21:32, 12 February 2021

Problem 31

In our number system the base is ten. If the base were changed to four you would count as follows: $1,2,3,10,11,12,13,20,21,22,23,30,\ldots$ The twentieth number would be:

$\textbf{(A)}\ 20 \qquad\textbf{(B)}\ 38 \qquad\textbf{(C)}\ 44 \qquad\textbf{(D)}\ 104 \qquad\textbf{(E)}\ 110$

Solution

The $20^{\text{th}}$ number will be the value of $20_{10}$ in base $4$. Thus, we see \[20_{10} = (1) \cdot 4^2 + (1) \cdot 4^1 + 0 \cdot 4^0\] \[= 110_{4}\]

$\boxed{E}$

~JustinLee2017

See Also

1956 AHSC (ProblemsAnswer KeyResources)
Preceded by
Problem 30
Followed by
Problem 32
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 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
All AHSME Problems and Solutions

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