Correct Answer: A

Rationale: Choice A represents no correlation between two variables as it states that as a student's class attendance decreases, the student's overall grade remains the same. This scenario shows no relationship between class attendance and grade. In contrast, choices B, C, and D show clear correlations between the variables mentioned. Choice B indicates a negative correlation between exercise hours and weight gain, choice C indicates a negative correlation between miles driven and gasoline in the tank, and choice D indicates a positive correlation between water intake and plant growth rate, making them all examples of correlated relationships.

Correct Answer: A

Rationale: The correct way to find the least common multiple is to list all the multiples of each number and then identify the smallest common multiple. Choice A is correct because it describes the correct process. Listing factors, as suggested in choice B, helps in finding the greatest common factor, not the least common multiple. Dividing the largest number by the smallest, as mentioned in choice C, does not help find the least common multiple. Multiplying the two numbers together, as stated in choice D, results in their least common multiple when the numbers have no common factors.

Correct Answer: A

Rationale: To find the length of the unknown leg (a) of a right triangle, use the Pythagorean theorem: a² + 9² = 19². Substitute the known values, solve for a: a² + 81 = 361. Subtract 81 from both sides to get a² = 280. Taking the square root of 280 gives a ≈ 16.7 feet. Therefore, the correct answer is 16.7 feet. Choice B (16.0 feet) is incorrect as it does not accurately round to the nearest tenth. Choice C (17.4 feet) and choice D (8.4 feet) are incorrect as they do not match the calculated value using the Pythagorean theorem.

Correct Answer: D

Rationale: The total volume of the room is 729 ft³ (9 ft * 9 ft * 9 ft). Each box has a volume of 8 ft³ (2 ft * 2 ft * 2 ft). Dividing the room's volume by the box volume, we get 729 ft³ / 8 ft³ ≈ 91.125. Since we can't have a fraction of a box, the maximum number of whole boxes that can fit is 92. Therefore, the correct answer is 92. Choice A (125) is incorrect as it does not result from the correct calculation. Choice B (64) and Choice C (18) are also incorrect and do not accurately represent the number of boxes that can fit in the room based on the given dimensions.

Correct Answer: A

Rationale: A common denominator is a shared multiple of the denominators in a set of fractions. It is necessary when adding or subtracting fractions to have a common denominator to ensure that the fractions can be combined accurately. Choice B is incorrect because the common denominator is related to the denominators, not the numerators. Choice C is incorrect because while the common denominator is the same in all fractions being added or subtracted, it is not necessarily a number that is the same in all fractions. Choice D is incorrect because a common denominator is a multiple of the denominators, not a number that divides evenly into both fractions.