Correct Answer: C

Rationale: The symbol '::' represents a proportion in which the first pair of numbers is related to the second pair of numbers. To solve for x in the proportion 2 : 5 :: 64 : x, you can set up a proportion equation: 2/5 = 64/x. Cross-multiplying gives you 2x = 5 * 64, which simplifies to 2x = 320. Dividing both sides by 2, you get x = 160. Therefore, x = 128 is the correct answer. Choice A (32) is incorrect as it is not the result of solving the proportion equation. Choice B (70) is incorrect as it is not related to the given proportion. Choice D (160) is a common mistake made by wrongly interpreting the equation; the correct value of x is 128.

Correct Answer: B

Rationale: The scale of 1:30 means that 1 inch on the plan represents 30 inches in actual size. If the width of the barn door on the plan is 3 inches, the actual width is calculated by multiplying 3 inches by the scale factor (30), giving 90 inches. To convert inches to feet, divide by 12 (since 12 inches = 1 foot), resulting in 90 inches · 12 = 7.5 feet. Therefore, the correct answer is 10 feet (option B), not 7.5 feet. Option A (90 inches) is the result before converting to feet, option C (9 feet) is the incorrect conversion if the initial calculation was done correctly, and option D (7.5 feet) is the incorrect conversion of the initial calculation.

Correct Answer: A

Rationale: To convert pounds to kilograms, you need to multiply the number of pounds by 0.4536. Therefore, to find out how many kilograms are in 20 pounds, you would calculate 20 x 0.4536 = 9.072 kilograms, which is approximately 9 kilograms. Choice A is correct. Choice B (16 kilograms), Choice C (44 kilograms), and Choice D (3 kilograms) are all incorrect conversions of pounds to kilograms.

Correct Answer: D

Rationale: To maintain the ratio of 2 parts fruit juice to 3 parts seltzer, for every 2 parts of fruit juice, Gwen will need 3 parts of seltzer. Since a gallon of fruit juice is equivalent to 4 quarts, she will need 3 quarts of seltzer for every 2 quarts of fruit juice. For 4 quarts of fruit juice, she will require 6 quarts of seltzer. Therefore, Gwen will need 6 quarts of seltzer to make the summer drink for her friends. Choice A (3 quarts) is incorrect because it does not account for the correct ratio. Choice B (4.5 quarts) is incorrect because it is not a whole number and does not align with the ratio provided. Choice C (5 quarts) is incorrect as it does not match the proportional ratio of fruit juice to seltzer required.

Correct Answer: D

Rationale: To multiply 54 by 45, you should multiply the two numbers together: 54 x 45 = 2430. The decimal point is placed after counting the total decimal places in the numbers being multiplied. As there are no decimal places in the numbers 54 and 45, the result is 2430, which is correctly expressed as 24.3 when considering the decimal point placement. Choice A (0.0243) and Choice B (0.243) are incorrect as they represent fractions of 2430. Choice C (2.43) is incorrect as it incorrectly places the decimal point one place before the actual result.