Correct Answer: A

Rationale: The correct answer is A: 175 mg. The vitamin originally contained 500 mg of calcium. After losing 325 mg, the remaining amount of calcium is calculated as 500 mg - 325 mg = 175 mg. Choice B (135 mg) is incorrect because the vitamin lost more calcium than that. Choices C (185 mg) and D (200 mg) are incorrect as they do not consider the amount of calcium lost from the original 500 mg.

Correct Answer: A

Rationale: The correct answer is A, which is 30.48. To convert inches to feet, since there are 12 inches in a foot, you need to multiply the conversion factor from inches to centimeters (2.54 cm) by the number of inches in a foot (12). This gives 30.48 cm in 1 foot. Choice B, 35, is incorrect as it does not follow the correct conversion. Choices C and D, 25 and 40 respectively, are also incorrect conversions and do not align with the conversion factors provided in the question.

Correct Answer: C

Rationale: To find x, set up the proportion and solve for x: 120/x = 40/0.5. Cross multiply to get 120 * 0.5 = 40x. This simplifies to 60 = 40x. Divide by 40 to isolate x, giving x = 60/40 = 1. Therefore, the correct answer is C, which is 1. Choice A (60) is incorrect because it does not match the correct calculation. Choice B (0) is incorrect as the calculation results in x = 1, not 0. Choice D (25) is incorrect as it does not match the correct calculation of x = 1.

Correct Answer: A

Rationale: To solve the proportion 7:5=91:x, cross multiply to get 7x = 5 * 91. Then, solve for x by dividing both sides by 7, which gives x = 65. Therefore, the correct answer is x=65. Choice B, x=55, is incorrect because it does not satisfy the proportion equation. Choices C and D, x=75 and x=85, are also incorrect as they do not match the calculated value of x when the proportion is solved.

Correct Answer: A

Rationale: Substitute x = -2 and m = -3 into the expression: (-2) * (-3) - 2 * (-3) = 6 + 6 = 12. Therefore, the correct answer is 12. The mistake in the other choices lies in the calculation. Choice B, 6, is the result of adding the two terms instead of subtracting the second term from the first. Choice C, 8, and Choice D, 10, are also incorrect as they do not follow the correct calculation process.