Correct Answer: A

Rationale: To convert milligrams (mg) to micrograms (mcg), you multiply by 1000 because 1 mg is equal to 1000 mcg. Therefore, 0.25 mg is equal to 250 mcg. Choices B, C, and D are incorrect as they do not consider the correct conversion factor.

Correct Answer: B

Rationale: The correct answer is B: 2.54 cm. One inch is equivalent to 2.54 centimeters in the metric system. This conversion factor is commonly used in converting measurements between the imperial and metric systems. Choice A (1.54 cm), Choice C (3.54 cm), and Choice D (4.54 cm) are incorrect conversions and do not represent the accurate metric equivalent of 1 inch.

Correct Answer: A

Rationale: To find the product of 0.5 and 20, you multiply them together. 0.5 x 20 = 10. This calculation involves multiplying a decimal (0.5) by a whole number (20). Choice A, '10', is the correct answer. Choice B, '15', is incorrect as it does not accurately represent the result of multiplying 0.5 by 20. Choices C and D, '20' and '25', are also incorrect as they do not reflect the correct calculation. This question assesses your ability to perform basic arithmetic operations involving decimals and whole numbers.

Correct Answer: B

Rationale: To convert milligrams to grams, you need to divide by 1,000 since there are 1,000 milligrams in 1 gram. Therefore, 5,000 milligrams is equal to 5 grams (5,000 · 1,000 = 5). Choice A, '50 grams,' is incorrect as it results from multiplying instead of dividing. Choice C, '500 grams,' is incorrect as it incorrectly multiplies the value. Choice D, '0.05 grams,' is incorrect as it is the result of dividing by 10 instead of 1,000.

Correct Answer: A

Rationale: The correct answer is A: 1 kilometer. 10^6 meters is equivalent to 1 kilometer, not 1 megameter. The prefix 'kilo-' represents a factor of 10^3 or one thousand, which is the appropriate conversion in this case. Choice B, 1 megameter, would be 10^6 meters squared. Choices C and D, 1 gigameter and 1 terameter, would represent even larger distances, as 'giga-' represents 10^9 and 'tera-' represents 10^12.