To convert the repeating decimal \( 0.18\overline{18} \) into a fraction, we can use an algebraic approach.
Let \( x = 0.181818...\)
Step 1: Multiply by a power of 10
Since the repeating part has two digits ("18"), we multiply \( x \) by \( 100 \) to shift the decimal point two places to the right:
\[ 100x = 18.181818... \]
Step 2: Set up an equation
Now we have two equations:
- \( x = 0.181818... \)
- \( 100x = 18.181818... \)
Step 3: Subtract the first equation from the second
We can subtract the first equation from the second to eliminate the repeating part:
\[ 100x - x = 18.181818... - 0.181818... \] \[ 99x = 18 \]
Step 4: Solve for \( x \)
Now, divide both sides by 99:
\[ x = \frac{18}{99} \]
Step 5: Simplify the fraction
To simplify \( \frac{18}{99} \), we need to find the greatest common divisor (GCD) of 18 and 99.
The GCD of 18 and 99 is 9. Now we divide both the numerator and the denominator by their GCD:
\[ \frac{18 \div 9}{99 \div 9} = \frac{2}{11} \]
Conclusion
Thus, the repeating decimal \( 0.18\overline{18} \) can be expressed as the rational number:
\[ \boxed{\frac{2}{11}} \]