Step 1: Identify the number of decimal places

The decimal 31.21 has 2 decimal places.

Step 2: Multiply by the appropriate power of 10

Multiply by 10² = 100 to eliminate the decimal point.

31.21 × 100 = 3121

Step 3: Write as a fraction

Step 4: Simplify the fraction

Find the greatest common divisor (GCD) of 3121 and 100.

GCD(3121, 100) = 1

Divide both the numerator and denominator by the GCD: