Step 1: Start with the fraction 40/10.

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

40 ÷ 10 = 4.0

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

4.0 × 100 = 400.0%

Final Answer: 40/10 as a percentage is 400.0%.