Correct Answer: A

Rationale: To add fractions, you need to find a common denominator. The common denominator for 8, 10, and 5 is 40. Then, convert each fraction: 7/8 = 35/40, 9/10 = 36/40, and 6/5 = 24/40. Now, add the fractions: 35/40 + 36/40 + 24/40 = 95/40, which simplifies to 2 15/40 or 2 3/8. Therefore, 7/8 + 9/10 + 6/5 = 3 & 39/40. Choice B is incorrect because it does not represent the correct addition of the fractions. Choice C is incorrect as it does not account for the whole number part. Choice D is incorrect as it is not the sum of the fractions and whole numbers.

Correct Answer: B

Rationale: To convert grams to milligrams, you need to multiply by 1,000 since there are 1,000 milligrams in a gram. Therefore, 7 grams x 1,000 = 7,000 mg. Choice A (700 mg) is incorrect as it represents 700 grams, not milligrams. Choice C (70 mg) is incorrect as it implies that 7 grams is equivalent to 70 milligrams, which is inaccurate. Choice D (0.007 mg) is also incorrect since it represents a fraction of a milligram, significantly less than the original 7 grams.

Correct Answer: B

Rationale: To convert grams to milligrams, you need to multiply by 1,000 because there are 1,000 milligrams in 1 gram. Therefore, to find out how many milligrams are in 3.4 grams, you multiply 3.4 by 1,000 which equals 3,400 mg. Choices A, C, and D are incorrect because they do not correctly convert grams to milligrams.

Correct Answer: C

Rationale: The metric system is based on powers of 10, making calculations and conversions easier because each unit increases or decreases by a factor of 10. This factor allows for a simple and consistent way to move between different units within the system. Choice A, 'The length of Napoleon's forearm' is incorrect as the metric system is not based on a physical attribute but on a standardized mathematical factor. Choice B, '2,' and Choice D, 'Atomic weight of helium,' are also incorrect as they do not align with the foundational principle of the metric system being based on powers of 10.

Correct Answer: A

Rationale: To convert 0.004 to a ratio, first express it as a fraction. 0.004 = 4/1000 = 1/250. Therefore, the ratio is 1:250. Choice A is the correct answer. Choices B, C, and D are incorrect ratios as they do not represent the equivalent fraction of 0.004.