Correct Answer: A

Rationale: To find out how many minutes Kevin will take to wash 100 cars, set up a proportion: 30 cars is to 15 minutes as 100 cars is to x minutes. Cross multiplying gives 30x = 1500. Solving for x, x = 1500 / 30 = 50. Therefore, it will take Kevin 50 minutes to wash 100 cars. Choice A is correct. Choice B, C, and D are incorrect as they do not correctly calculate the time needed based on the given information.

Correct Answer: C

Rationale: To calculate the total number of words typed in 20 minutes, multiply the typing speed per minute (45 words) by the duration in minutes (20 minutes): 45 words/min 20 min = 900 words. Therefore, the correct answer is 900 words. Choices A, B, and D are incorrect because they do not reflect the accurate calculation based on the given information.

Correct Answer: A

Rationale: To subtract mixed numbers, find a common denominator. In this case, the common denominator is 20. Convert 15 3/4 to 15 15/20. Then, subtract 15 15/20 - 8 8/20 = 7 7/20. Therefore, the correct answer is A. Choice B is incorrect as it does not match the result of the subtraction. Choice C is incorrect as it is not the result of the subtraction. Choice D is incorrect as it represents the second number being subtracted, not the result of the subtraction.

Correct Answer: A

Rationale: To add mixed numbers, first add the fractions: 1/8 + 1/4 = 3/8. Then, add the whole numbers: 3 + 1 = 4. Therefore, 3 1/8 + 1 1/4 = 4 3/8. Choice B (4 1/2) is incorrect because the fractions were not added correctly, leading to an incorrect result. Choice C (4 3/4) is incorrect as it does not represent the correct sum of the two mixed numbers. Choice D (5 1/4) is incorrect as it provides a result that is higher than the correct sum of the mixed numbers.

Correct Answer: A

Rationale: When dividing fractions, you multiply by the reciprocal of the divisor. To divide 5 3/4 by 1/2, you multiply 5 3/4 by 2/1 (reciprocal of 1/2) to get 23/4 * 2/1 = 46/4 = 11 1/2. Therefore, the correct answer is A. Choice B (2 & 3/8) is incorrect as it does not result from dividing 5 3/4 by 1/2. Choice C (3 & 1/8) is incorrect as well. Choice D (18) is not the correct result of the division performed.