Step 1: Identify the number of decimal places

The decimal 20.405 has 3 decimal places.

Step 2: Multiply by the appropriate power of 10

Multiply by 10³ = 1000 to eliminate the decimal point.

20.405 × 1000 = 20405

Step 3: Write as a fraction

Step 4: Simplify the fraction

Find the greatest common divisor (GCD) of 20405 and 1000.

GCD(20405, 1000) = 5

Divide both the numerator and denominator by the GCD: