Correct Answer: C

Rationale: To find out how much ammonia is needed for 230 gallons of cleaning solution, you multiply the amount of ammonia needed per gallon by the total gallons of solution required. Therefore, 230 gallons * 6 oz/gallon = 1380 oz of ammonia. Option A ('1380 gallons') and Option B ('6900 gallons') are incorrect as the question asks for the amount of ammonia needed, not the total volume of cleaning solution. Option D ('1400 oz') is incorrect as it does not correctly calculate the amount of ammonia required based on the given information.

Correct Answer: D

Rationale: The correct answer is 25 g. Pencils are usually lightweight, and their weight is measured in grams. 25 kg (choice A) is too heavy for a pencil. 25 cm (choice B) is a unit of length, not weight. 25 mg (choice C) is too light for a pencil, as pencils typically weigh more than milligrams.

Correct Answer: C

Rationale: A composite number is a positive integer greater than one that has more than two factors. Choice A is incorrect because a number with only two factors is a prime number. Choice B is incorrect as being a fraction does not define a composite number. Choice D is incorrect because a number with exactly two factors is a prime number, not a composite number.

Correct Answer: C

Rationale: To find the amount the friend paid, you can set up the equation 2x - 2000 = 48000, where x represents the amount the friend paid. Solving this equation gives x = $25,000. Therefore, the friend paid $25,000. Choice A ($23,000) is incorrect because it does not account for the $2,000 difference mentioned in the question. Choice B ($46,000) is incorrect because it is double the amount needed. Choice D ($50,000) is incorrect as it does not consider the $2,000 less mentioned in the question.

Correct Answer: C

Rationale: The baby's measured weight is the dependent variable as it depends on the time intervals.