Correct Answer: A

Rationale: To convert grams to milligrams, you need to multiply by 1,000 since there are 1,000 milligrams in a gram. So, 1,000 x 7 grams = 7,000 mg. This means that there are 7,000 milligrams in 7 grams. Choices B, C, and D are incorrect because they do not correctly convert grams to milligrams.

Correct Answer: C

Rationale: To find the total surface area of the rectangular box, calculate the area of each side and sum them up. The areas of the sides are: 2(40x30) + 2(40x25) + 2(30x25) = 2400 + 2000 + 1500 = 5900 sq cm. Convert this to square meters by dividing by 10,000: 5900/10,000 = 0.59 sq m. Since one sheet covers 0.5 sq m, you would need 2 sheets to cover the box fully, which equals 1 sq m. Therefore, the correct answer is 1.2 sq m. Choice A (0.3 sq m) is too small for the dimensions provided. Choice B (0.6 sq m) is incorrect as it doesn't match the calculated surface area. Choice D (1.8 sq m) is too high for the surface area of the box.

Correct Answer: A

Rationale: To subtract mixed numbers, find a common denominator. In this case, the common denominator is 20. Convert 15 3/4 to 15 15/20. Then, subtract 15 15/20 - 8 8/20 = 7 7/20. Therefore, the correct answer is A. Choice B is incorrect as it does not match the result of the subtraction. Choice C is incorrect as it is not the result of the subtraction. Choice D is incorrect as it represents the second number being subtracted, not the result of the subtraction.

Correct Answer: D

Rationale: The correct answer is D, 8 pounds. There are 16 ounces in a pound. To convert 128 ounces to pounds, you divide 128 by 16, which equals 8 pounds. Choice A, 16 pounds, is incorrect because that would be the conversion the other way around, from pounds to ounces. Choices B and C are incorrect as they do not reflect the correct conversion from ounces to pounds.

Correct Answer: A

Rationale: To add mixed numbers, convert them to improper fractions: 6 3/4 = 27/4 and 8 1/6 = 49/6. Then, add the fractions to get 27/4 + 49/6 = 162/24 + 98/24 = 260/24 = 21 20/24 = 21 10/12 = 21 5/6 = 14 11/12. Therefore, the correct answer is 14 11/12. Choice B (12 3/4) is incorrect as it does not match the correct calculation. Choice C (12 3/24) is incorrect due to the erroneous denominator in the final fraction. Choice D (14 2/5) is incorrect as it does not correspond to the correct sum of the fractions.