Express the decimal number 0.125 as a percentage.

Introduction / Context:
This question tests the basic but important skill of converting a decimal number into a percentage. Being able to move comfortably between fractions, decimals and percentages is fundamental in quantitative aptitude, finance, data interpretation and many everyday calculations. Here, the decimal 0.125 must be written in percentage form.

Given Data / Assumptions:

The decimal given is 0.125.

We need to express this value as an equivalent percentage.

No rounding is required because 0.125 converts neatly to a terminating percentage.

The percentage symbol % will be included in the final answer.

Concept / Approach:
To convert a decimal to a percentage, we use the rule: percentage = decimal * 100. This is because percent literally means per hundred. Another way is to first convert the decimal into a fraction and then into a percentage. For 0.125, it is easy to recognize that it equals 1 / 8. The fraction 1 / 8 can then be converted to a percentage by multiplying by 100. Both approaches lead to the same numerical result and strengthen the understanding of how decimals, fractions and percentages relate.

Step-by-Step Solution:
We are given the decimal 0.125.Method 1 (direct decimal to percent): Percentage = 0.125 * 100.0.125 * 100 = 12.5.So the required percentage is 12.5%.Method 2 (via fraction): 0.125 = 125 / 1000.Simplify 125 / 1000 by dividing numerator and denominator by 125 to get 1 / 8.Now multiply by 100 to convert to percent: (1 / 8) * 100 = 12.5.Therefore, the decimal 0.125 equals 12.5%.

Verification / Alternative check:
We can check the consistency by reversing the process. Take 12.5% and convert it back to decimal. First write 12.5% as 12.5 / 100. Now 12.5 / 100 = 0.125. This matches the original decimal given in the problem, so our conversion is confirmed to be correct. This forward and backward check is a good habit for exam practice.

Why Other Options Are Wrong:

12% is slightly smaller than 12.5% and corresponds to 0.12, not 0.125.

13% equals 0.13 as a decimal and therefore is larger than 0.125.

13.5% equals 0.135 and again does not match 0.125.

1.25% equals 0.0125, which is ten times smaller than 0.125.

Common Pitfalls:
Some students forget to multiply by 100 and instead divide by 100, ending up with 0.00125. Others may misplace the decimal point and write 1.25% instead of 12.5%. Another pitfall is rounding too early or incorrectly simplifying the fraction representation. To avoid these errors, always follow the simple rule: to convert a decimal to a percentage, multiply by 100 and attach the percent symbol at the end.

Final Answer:
The decimal number 0.125 expressed as a percentage is 12.5%.