When the ratio 5 : 4 is written as a fraction and then expressed as a percentage, what percent does it represent?

Introduction:
This question checks your ability to convert a ratio into a fraction and then into a percentage. Ratios, fractions, and percentages are closely related, and quick movement between these three forms is useful in many aptitude topics including profit and loss, mixtures, and data interpretation.

Given Data / Assumptions:
Ratio given is 5 : 4.
We interpret this ratio as the fraction 5 divided by 4.
We must express this fraction as a percentage.
No other contextual constraints are given, so it is a direct number conversion problem.

Concept / Approach:
A ratio a : b can be interpreted as the fraction a / b, provided the question specifies or implies this direction. To convert a fraction to a percentage, we multiply by 100. So here we compute (5 / 4) * 100. This is a simple arithmetic step once the ratio is seen as a fraction.

Step-by-Step Solution:
Start from the ratio 5 : 4. Interpret it as the fraction 5 / 4. Compute 5 / 4. This equals 1.25. To convert a fraction or decimal to a percentage, multiply by 100. Percentage = 1.25 * 100. 1.25 * 100 = 125. Therefore, 5 : 4 expressed as a percentage is 125%.
Verification / Alternative check:
We can also think of 5 as being 25% more than 4. Since 25% of 4 is 1, adding this to 4 gives 5. So 5 is 125% of 4. This reasoning matches the numerical computation and provides an intuitive check that 5/4 corresponds to 125%.

Why Other Options Are Wrong:
40% and 80% are less than 100% and would correspond to fractions smaller than 1, while 5/4 is greater than 1. 100% would represent equality (5 equals 4), which is not true. 150% would be 1.5 times 4, that is 6, not 5. Therefore only 125% correctly represents the ratio 5 : 4.

Common Pitfalls:
A common mistake is to interpret the ratio 5 : 4 as 4/5 instead of 5/4. Another error is to forget the multiplication by 100 when converting a decimal to a percentage. Some candidates also confuse percent increase with the underlying percent of the original quantity. Keeping the direction of the ratio and the conversion steps clear avoids these issues.

Final Answer:
The ratio 5 : 4 expressed as a percentage is 125%.