Correct Answer: A

Rationale: The correct answer is 'Multiplication.' In the expression 8 + 5 * 3, according to the order of operations (PEMDAS), multiplication should be done before addition. PEMDAS stands for Parentheses, Exponents, Multiplication and Division (from left to right), and Addition and Subtraction (from left to right). Therefore, the multiplication operation should be completed first, making 5 * 3 equal to 15, and then the addition operation should be conducted to get the final result of 8 + 15, which equals 23. Choices B, C, and D are incorrect because in this expression, multiplication takes precedence over addition, division, and subtraction according to the order of operations.

Correct Answer: D

Rationale: The factors of 12 are numbers that divide evenly into 12 without leaving a remainder. The correct factors of 12 are 1, 2, 3, 4, 6, and 12. Choice A (12, 24, 36) is incorrect as only 12 is a factor of 12. Choice B (1, 2, 4, 6, 12) includes all the correct factors of 12. Choice C (12, 24, 36, 48) is incorrect as 24, 36, and 48 are not factors of 12.

Correct Answer: C

Rationale: A valid hypothesis must be a testable statement that predicts a relationship between variables. Option C is the only statement that presents a clear cause-and-effect relationship between the amount of poison given and the time it takes for the rat to die. Option A is descriptive without predicting an outcome, option B is a question rather than a statement, and option D is a general fact about poison and rats, lacking a specific hypothesis for testing.

Correct Answer: B

Rationale: To find the area of a rectangle, you multiply its length by its width. In this case, the length is 5 cm and the width is 4 cm. So, Area = length * width = 5 cm * 4 cm = 20 cm². Therefore, the correct answer is 20 cm². Choice A (9 cm²), Choice C (10 cm²), and Choice D (25 cm²) are incorrect as they do not result from the correct calculation of multiplying the length and width of the rectangle.

Correct Answer: B

Rationale: To convert miles to kilometers, we use the conversion factor of 1 mile ≈ 1.60934 km. Therefore, 4.67 miles * 1.60934 km/mile = 7.514 km. When rounded to three significant digits, the answer is 7.51 km. Choice A of 7.514 km is the correct conversion, but the question asked for the answer to be rounded to three significant digits, making choice B, 7.51 km, the most precise and correct option. Choices C and D are incorrect conversions and do not match the correct conversion of 4.67 miles to kilometers.