Repeat#3

42.34 78 = a b c \large 42.34\overline{78} = a\frac bc

Where a b c a\dfrac bc is a mixed fraction and a , b a,b and c c are integers with b , c b,c coprime. Find a + b + c a+b+c


The answer is 1154.

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1 solution

Arjen Vreugdenhil
Jan 10, 2018

The general approach is as follows: Let the given decimal number x x consist of

  • whole part w w ;

  • non-repeating part of d d digits, with integer value n n ;

  • repeating part of e e digits, with integer value r r .

Then the fraction is equal to x = w + ( 1 0 e 1 ) n + r 1 0 d ( 1 0 e 1 ) . x = w + \frac{(10^e - 1)n + r}{10^d(10^e - 1)}. The fraction must be further be reduced by dividing out common factors (typically powers of 2 and 5, or 3, 11, 13, 37.)


Application

In this problem, w = 42 w = 42 , d = 2 d = 2 , n = 34 n = 34 , e = 2 e = 2 , r = 78 r = 78 , so that x = 42 + 99 34 + 78 100 99 = 42 3444 9900 . x = 42 + \frac{99\cdot 34 + 78}{100\cdot 99} = 42\frac{3444}{9900}. After dividing out the common factor 2 2 3 = 12 2^2\cdot 3 = 12 , we find x = 42 287 825 , x = 42\frac{287}{825}, making the final answer 42 + 287 + 825 = 1154 42 + 287 + 825 = \boxed{1154} .

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