Correct Answer: A

Rationale: To find the total distance traveled, you need to multiply the speed of the train by the time it travels. So, 80 km/h * 3 hours = 240 kilometers. Therefore, the correct answer is 240 kilometers. Choice B (160 kilometers) is incorrect because it is the result of multiplying the speed by 2 hours instead of 3. Choice C (240 kilometers) is the same as the correct answer, making it redundant. Choice D (210 kilometers) is incorrect as it is the result of multiplying the speed by 2.5 hours instead of 3.

Correct Answer: B

Rationale: The normal range for potassium levels is typically considered to be between 3.5 to 5.3 mmol/L. In this case, the potassium level of 4.5 mmol/L falls within this normal range. Therefore, the correct answer is that it is within the normal range (Choice B). Choice A is incorrect as 4.5 mmol/L is not too low. Choice C is also incorrect as 4.5 mmol/L is not too high. Choice D is incorrect as the given information is sufficient to determine that the potassium level is within the normal range.

Correct Answer: D

Rationale: To determine the highest number among 0.077, 0.777, 0.08, and 0.87, we compare the numbers. 0.87 is greater than 0.777, 0.08, and 0.077, making it the highest number. Choice A (0.077), Choice B (0.777), and Choice C (0.08) are lower numbers compared to 0.87, so they are incorrect.

Correct Answer: D

Rationale: To convert 5 3/4 to a decimal, divide the numerator (3) by the denominator (4) to get 0.75. Adding this to the whole number 5 results in 5.75. When rounding to the nearest tenth, 5.75 rounds to 5.8. Choice A, 5.75, is the exact conversion before rounding, so it is incorrect. Choice B, 5.7, is incorrect because it does not account for the 0.05 difference when rounding. Choice C, 6, is incorrect as it is the closest whole number but not a decimal approximation. Therefore, the correct answer is 5.8.

Correct Answer: D

Rationale: The runner left at 7:45 and returned at 10:00, which means he ran for 2 hours and 15 minutes (10:00 - 7:45). At an average speed of 6 mph, in 2.25 hours, he would have covered 6 mph * 2.25 hours = 13.5 miles. Therefore, the correct answer is 13.5 miles. Choices A, B, and C are incorrect because they incorrectly calculate the distance based on the time and speed provided in the question.