Correct Answer: A

Rationale: The correct expression for the sum of three times a number and eight times a different number is given by 3x + 8y. This represents adding three times the variable x (3x) to eight times the variable y (8y). Choice B (8x + 3x) is incorrect as it represents adding eight times x to three times x, which is redundant. Choice C (3x - 8y) is incorrect because it represents subtracting eight times y from three times x, not their sum. Choice D (8x - 3y) is also incorrect as it represents subtracting three times y from eight times x, not their sum.

Correct Answer: B

Rationale: To find the sale price after a 15% discount, you calculate 15% of $78, which is $11.70. Subtracting $11.70 from the original price gives $66.30. Since the price is typically rounded, the estimated sale price is $66. Choice A, $12, is too low and does not reflect a 15% discount off $78. Choice C, $22, and choice D, $69, are also incorrect as they do not accurately estimate the sale price after a 15% discount.

Correct Answer: A

Rationale: The equation D=2R means that D equals 2 times R, which translates to D being twice the value of R. Therefore, choice A, 'D is twice as much as R,' is the correct representation of the relationship between D and R. Choice B, 'R is twice as much as D,' incorrectly reverses the roles of D and R. Choice C, 'R is two times D,' incorrectly states the relationship between R and D. Choice D, 'D is two more than R,' does not accurately reflect the relationship presented in the equation.

Correct Answer: D

Rationale: To find the cost of one syringe, divide the total cost by the number of syringes: $660.00 · 55 = $12. Therefore, the cost of four syringes is 4 x $12 = $48. Choices A, B, and C are incorrect because they do not correctly calculate the cost per syringe or the total cost of four syringes.

Correct Answer: D

Rationale: To find the area of a circle, we use the formula A = πr², where r is the radius of the circle. In this case, the diameter is 9 inches, so the radius is half of the diameter, which is 4.5 inches. Substituting the radius into the formula, we get A = π(4.5)² = 20.25 πin². Therefore, the correct answer is 20.25 πin². Choices A, B, and C are incorrect because they do not correctly calculate the area using the radius of the circle.