Tiny proportion in mixed units: What percent of 7.2 kg is 18 grams? (Use 1 kg = 1000 g)

Introduction / Context:
This tests unit conversion and percentage computation. When quantities are given in different units (kilograms and grams), convert them to a common unit before calculating the percentage, to avoid scale mismatches.

Given Data / Assumptions:

• Total = 7.2 kg = 7200 g.
• Part = 18 g.

Concept / Approach:
Percent = (part / whole) * 100%. After converting 7.2 kg to 7200 g, compute 18/7200 and multiply by 100 to get the percentage. Keep an eye on decimal placement because the values are small.

Step-by-Step Solution:

Verification / Alternative check:
Reduce 18/7200 = 1/400; (1/400)*100% = 0.25%. This fractional route provides a neat mental math check.

Why Other Options Are Wrong:
0.025% and 0.0025% are off by factors of 10 or 100; 2.5% and 25% are large by orders of magnitude relative to 18 out of 7200.

Common Pitfalls:
Forgetting to convert kilograms to grams or mixing up numerator and denominator when forming the percentage fraction.

Final Answer:
0.25%