What percentage of 7.2 kilograms is equal to 18 grams?

Introduction:
This question checks your understanding of basic percentage calculation and unit conversion between kilograms and grams. Many quantitative aptitude problems involve converting units properly before applying percentage formulas, so this is an important foundation skill.

Given Data / Assumptions:
Total quantity = 7.2 kilograms.
Part of this quantity = 18 grams.
We need to express 18 grams as a percentage of 7.2 kilograms.
We use the standard relationship 1 kilogram = 1000 grams.

Concept / Approach:
Percent is calculated as (part / whole) * 100. However, the part and the whole must be in the same unit. Here the part is given in grams and the whole in kilograms. Therefore we first convert 7.2 kilograms into grams, and then use the percentage formula. This ensures there is no inconsistency in units that might lead to wrong answers.

Step-by-Step Solution:
Convert 7.2 kilograms to grams: 7.2 * 1000 = 7200 grams. Now treat 18 grams as the part and 7200 grams as the whole. Percentage = (part / whole) * 100. So percentage = (18 / 7200) * 100. Compute 18 / 7200 = 0.0025. Now multiply by 100: 0.0025 * 100 = 0.25. Therefore, 18 grams is 0.25% of 7.2 kilograms.
Verification / Alternative check:
We can check the answer by reversing the calculation. Take 0.25% of 7.2 kilograms. First convert 0.25% to a fraction: 0.25% = 0.25 / 100 = 0.0025. Multiply this by 7.2 kilograms: 7.2 * 0.0025 = 0.018 kilograms. Convert 0.018 kilograms to grams: 0.018 * 1000 = 18 grams. This matches the given part, confirming that the percentage is correct.

Why Other Options Are Wrong:
0.5%, 0.75%, 1%, and 2.5% all represent larger fractions of the whole. If you compute these percentages of 7.2 kilograms, you would get values significantly larger than 18 grams. For example, 1% of 7.2 kilograms is 72 grams, which is far greater than 18 grams. These options likely arise if a candidate forgets the kilogram to gram conversion or misplaces the decimal point when multiplying by 100.

Common Pitfalls:
A frequent mistake is to divide 7.2 by 18 instead of 18 by 7.2, or to forget to convert kilograms into grams. Another common error is mishandling decimal places when multiplying or dividing by powers of 10. Remember that unit consistency and careful handling of decimal values are critical in percentage problems.

Final Answer:
18 grams is 0.25% of 7.2 kilograms.