Correct Answer: D

Rationale: To simplify the expression, first multiply 6.4 by 2.8 to get 17.92. Then, divide the result by 0.4 to find the final answer. Therefore, (6.4)(2.8) · 0.4 equals 44.8. Choices A, B, and C are incorrect because they do not represent the correct result of the given expression.

Correct Answer: D

Rationale: The correct answer is D: 4.412 10^3. To simplify the expression, rewrite 4.71 10^3 as 47.1 10^2. Subtract the values in front of 10^2: 47.1 - 2.98 = 44.12. Rewriting this gives 44.12 10^2 = 4.412 10^3. Choice A is incorrect as it does not account for the correct subtraction result. Choice B is incorrect as it does not correctly simplify the expression. Choice C is incorrect as it provides an incorrect power of 10 in the simplified expression.

Correct Answer: A

Rationale: To find the width of the rectangular field, use the formula for the area of a rectangle: A = length width. Given that the length is three times the width, you have A = 3w w. Substituting the given area, 1452 = 3w^2. Solving for w, you get 484 = w^2. Taking the square root gives ±22, but since the width must be positive, the width of the field is 22 feet. Choice B, 44 feet, is incorrect because it represents the length, not the width. Choice C, 242 feet, is incorrect as it is not a factor of the area. Choice D, 1452 feet, is incorrect as it represents the total area of the field, not the width.

Correct Answer: B

Rationale: To simplify the expression, apply the order of operations (PEMDAS). Begin by squaring -2 to get 4. Then perform the multiplication and subtraction within parentheses: 52(3) + 3(4)/4 + 9 - 2(5 - 8) = 156 + 12/4 + 9 - 2(3) = 156 + 3 + 9 - 6 = 168 + 3 - 6 = 171 - 6 = 165. Therefore, the correct simplified expression is 165, which is equivalent to 87/19. Choices A, C, and D are incorrect because they do not represent the accurate simplification of the given expression.

Correct Answer: D

Rationale: To solve for x, multiply both sides by the reciprocal of 5/4 to isolate x. (4/5)(5/4)x = (4/5)20; x = 16. Therefore, the correct answer is 32. Choice A (8), Choice B (16), and Choice C (24) are incorrect as they do not represent the correct value of x obtained after correctly simplifying the expression.