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How do you convert

$14\frac{8}{13}$

into base 3?

I was able to convert $\frac{3}{7}$ into base 3 by constantly multiplying by 3 and dividing the numerator by denominator until I finally got a repetition, but this method doesn't seem to work for $14\frac{8}{13}$.

The correct answer is supposed to be $112.\overline{121}_{3}$

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Um, fractions work the same in all bases. There's an integer above the fraction bar and an integer below. You can write those integers in any basis you like; doing that is independent of the fact that they're in a fraction. –  Henning Makholm Nov 5 '11 at 15:33
    
I'm not sure if I understand, are you saying I can just convert the top number and the bottom number seperately? –  Arvin Nov 5 '11 at 15:35
    
Sorry, I didn't see the supposed correct answer. I was confused because you described the input as a "base 10 fraction", and the equivalent of that in base 3 would be $\left[112\frac{22}{111}\right]_3$. You can do long division $22\div 111$ in base 3 to get the positional notation. –  Henning Makholm Nov 5 '11 at 15:52
    
Thanks for that, so I can convert the 14 seperately to the $\frac{8}{13}$ since they are just two numbers multiplied –  Arvin Nov 5 '11 at 16:05
    
Oops, yes, I meant added. –  Arvin Nov 5 '11 at 17:57

2 Answers 2

up vote 1 down vote accepted

Just like you convert a fraction to decimal. $8\cdot 3=24=13(1)+11,$ so the first digit (ternit?) is $1. \ \ 11\cdot 3=33=13(2)+7,$ so the second digit is $2. \ \ 3\cdot 7=21=13(1)+8$ and so on. I get $112.\overline{121}_{3}$

Alternately you can notice that $\frac{8}{13}=\frac{16}{3^3-1}$, so the repeat is $3$ digits long and is $16_{10}=121_3$

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Is your answer only for $\frac{8}{3}$? –  Arvin Nov 5 '11 at 15:50
    
Thanks, no worries, I am able to convert the 14 into base 3, I didn't know you were supposed to do the 14 and the fraction separately. –  Arvin Nov 5 '11 at 16:12
    
@Arvin: I was only describing how to do the fraction, $\frac{8}{13}$, not $\frac{8}{3}$. I then appended the result for the whole number (now corrected to $112_3$) –  Ross Millikan Nov 5 '11 at 16:16
    
Typo, I meant to write $\frac{8}{13}$. Thanks! –  Arvin Nov 5 '11 at 17:58

You convert 8 and 13 into base 3, and do a long division in that base,

          0.202           8 = 101
      ------------           -----
  111 ) 101              13 = 111
         22.2
         -----
          1.100
          0.222
            101  (repeats on three places)

So the answer is 112.202 202 202

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