Solving for 100x: A Math Puzzle

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SUMMARY

The discussion focuses on the mathematical technique for converting repeating, non-terminating decimals into fractional form, specifically using the example of x = 0.91919191. By multiplying by 100, the equation 100x - x = 91 illustrates that any periodic decimal can be expressed as a fraction, confirming that periodic decimals are rational numbers. The final result of this method is x = 91/99, providing a clear and concise representation of the original decimal.

PREREQUISITES
  • Understanding of periodic decimals
  • Basic algebraic manipulation skills
  • Familiarity with rational numbers
  • Knowledge of mathematical proofs
NEXT STEPS
  • Study the properties of rational numbers and their decimal representations
  • Explore techniques for converting other repeating decimals into fractions
  • Learn about mathematical proofs related to number theory
  • Investigate the implications of periodic decimals in real-world applications
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Students, educators, and anyone interested in understanding the conversion of repeating decimals to fractions and the underlying mathematical principles involved.

thomas49th
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Hi, I recall a thingy when you have somthing like

x = 0.91919191

then you go 100x = 91.919191
100x - x = 91

When do you use this? It's in conjuction with somthing else... looked in my textbook can't find it.

Thanks
 
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Personally, I use that when I have a repeating, non-terminating decimal that I want to get in fractional form so it looks prettier in an equation.
 
Why should you care "when is it used"?
It is a wrong question; the technique is never "used"; rather, it illustrates how you may rewrite a periodic decimal as a fraction.

That is, the technique amounts to a constructive PROOF of a certain mathematical proposition:
namely that any periodic decimal can be written as a fraction between two natural numbers, i.e a periodic decimal is necessarily a rational number.
 
100x - x=99x=91

x=91/99

Thats why its used, to get urself a fraction.
 

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