Fractions and Decimals

Evaluate the sum of coprime positive integers p + q p+q , where p q = 0. 0123456789 \frac{p}{q}=0.\overline{0123456789} (the recurring decimal composed of the 10 10 digits of base 10 10 repeating infinitely).

Details & Assumptions :

  • If you believe that no such fraction exists, enter 1 -1 as your answer.


The answer is 1124828532.

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1 solution

Alex Delhumeau
Feb 20, 2017

The rational number < 1 < 1 that will expand to the sequence 0 , 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 repeated infinitely many times when converted to decimal form is 13717421 1111111111 \large{\frac{13717421}{1111111111}} 13717421 + 1111111111 = 1124828532 \rightarrow 13717421+1111111111=\boxed{1124828532} .

Proof:

Let S = 0. 0123456789 S = 0.\overline{0123456789} . Then 1 0 10 S = 123456789. 0123456789 10^{10}*S = 123456789.\overline{0123456789} .

Hence by subtraction, ( 1 0 10 1 ) S = 123456789 S = 123456789 9999999999 = 41152263 3333333333 = 13717421 1111111111 (10^{10}-1)S = 123456789 \rightarrow S = \large{\frac{123456789}{9999999999}=\frac{41152263}{3333333333}=\frac{13717421}{1111111111}} .

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