Correct Answer: A

Rationale: To solve the equation 5x + 10 = 20, first subtract 10 from both sides to isolate the term with x: 5x = 10. Then, divide by 5 on both sides to find the value of x: x = 2. Therefore, the correct answer is A. Choice B is incorrect because x is not equal to 2 but 4. Choice C is incorrect as x is not equal to 5. Choice D is incorrect as x is not equal to 7.

Correct Answer: C

Rationale: To solve for x, cross-multiply: x/250 = 3/500. This simplifies to x = 1.5. Therefore, the correct answer is 1.5. Choice A (150) is incorrect because it does not account for the division by 250. Choice B (25.5) is incorrect as it is not the correct result of the calculation. Choice D (60) is incorrect as it is not the correct result of the calculation either.

Correct Answer: D

Rationale: To find 80% of $500, you multiply 0.8 by 500. Therefore, 0.8 x 500 = $400. This means that option D, $400, is the correct answer. Option A, $425, is incorrect because it is higher than the calculated value. Option B, $450, is also higher than the correct answer. Option C, $350, is lower than the calculated value. Hence, the correct answer is D, $400.

Correct Answer: C

Rationale: The correct answer is 7.3. To subtract 13.4 from 20.7, you align the decimal points and subtract each place value: 0.7 - 0.4 = 0.3, and 2 - 1 = 1. Therefore, 20.7 - 13.4 = 7.3. Choices A, B, and D are incorrect because they do not provide the accurate result of this subtraction.

Correct Answer: A

Rationale: 32 · (8\9) is the same as 32 (9\8) = 36.