Math Problem Statement

Show that the following number is rational by writing it as a ratio of two integers.

0.71717171…

Solution

The number 0.717171710.71717171\ldots is a repeating decimal, and we can express it as a fraction, proving that it is rational. Here's how we do it step by step:

Let x=0.71717171x = 0.71717171\ldots

Step 1: Multiply both sides by 100

Since the decimal repeats every two digits, we multiply by 100100 to shift the decimal point two places to the right:

100x=71.71717171100x = 71.71717171\ldots

Step 2: Subtract the original equation from this new equation

Now subtract x=0.71717171x = 0.71717171\ldots from 100x=71.71717171100x = 71.71717171\ldots:

100xx=71.717171710.71717171100x - x = 71.71717171\ldots - 0.71717171\ldots

This simplifies to:

99x=7199x = 71

Step 3: Solve for xx

Now, solve for xx by dividing both sides by 99:

x=7199x = \frac{71}{99}

Thus, 0.717171710.71717171\ldots is equal to 7199\frac{71}{99}, which is a ratio of two integers, so it is a rational number.

Would you like further details or clarifications?


Here are 5 related questions for further exploration:

  1. How can we convert other repeating decimals into fractions?
  2. What is the difference between rational and irrational numbers?
  3. Can a repeating decimal ever be an irrational number?
  4. How would you convert 0.252525250.25252525\ldots into a fraction?
  5. What properties do rational numbers have in relation to repeating decimals?

Tip: A decimal that repeats after a fixed number of digits is always a rational number.

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Math Problem Analysis

Mathematical Concepts

Algebra
Repeating Decimals
Rational Numbers

Formulas

x = repeating decimal, 100x = shifted decimal, solve for x using subtraction

Theorems

Rational Number Theorem: A decimal that repeats is always rational

Suitable Grade Level

Grades 8-10