Step 1: Start with the fraction 21/28.

Step 2: To convert a fraction into a percentage, divide the numerator by the denominator.

21 ÷ 28 = 0.75

Step 3: Multiply the result by 100 to get the percentage.

0.75 × 100 = 75.0%

Final Answer: 21/28 as a percentage is 75.0%.