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: C

Rationale: To solve the equation 2x - 7 = 9, first, add 7 to both sides to isolate the variable: 2x = 16. Then, divide by 2 to solve for x: x = 8. Choice A (x = 10) is incorrect because the solution is x = 8, not 10. Choice B (x = 7) is incorrect as it does not correctly solve the equation. Choice D (x = 5) is incorrect as it does not yield the correct solution for x.

Correct Answer: D

Rationale: To solve for x when x/5 = 3/10, you need to cross-multiply. This gives you 10x = 5 3. Simplifying further, you get x = 15/10, which reduces to x = 1.5. Therefore, the correct answer is x = 1.5. Choices A, B, and C are incorrect because they do not match the correct calculation for x.

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: B

Rationale: To convert a fraction to a decimal, divide the numerator by the denominator. In this case, 1 · 5 = 0.2. Therefore, the correct answer is B. Choice A (0.5) is incorrect because the decimal form of 1/5 is not 0.5. Choice C (1.5) is incorrect as it is the sum of 1 and 0.5, not the decimal form of 1/5. Choice D (0.15) is incorrect as it is the decimal form of 15/100, not 1/5.