Step 1: Identify the number of decimal places

The decimal 0.663984 has 6 decimal places.

Step 2: Multiply by the appropriate power of 10

Multiply by 10⁶ = 1000000 to eliminate the decimal point.

0.663984 × 1000000 = 663984

Step 3: Write as a fraction

Step 4: Simplify the fraction

Find the greatest common divisor (GCD) of 663984 and 1000000.

GCD(663984, 1000000) = 16

Divide both the numerator and denominator by the GCD: