To convert the decimal 0.72 to a rational number, you can express it as a fraction. Since 0.72 has two decimal places, you can write it as:
\[ 0.72 = \frac{72}{100} \]
Next, simplify the fraction by finding the greatest common divisor (GCD) of 72 and 100. The GCD of 72 and 100 is 4. Now divide both the numerator and the denominator by their GCD:
\[ \frac{72 \div 4}{100 \div 4} = \frac{18}{25} \]
Thus, the simplest form of the rational number is:
\[ \frac{18}{25} \]