This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Dental
[{'content': 'The length of human pregnancies from conception to birth can be approximated a normal distribution with a mean of 265 days and a standard deviation of 15 days. What percentage of all pregnancies will last between 250 and 280 days? \nSelect and explain. \nA. 38%, B. 54%, C. 58%, D. 68%', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Normal/Gaussian curve:\nIs ‘bilaterally symmetrical, bell-shaped’\nIs bases on mean (µ) and standard deviation (σ)\xa0\nMean, Median and Mode coincide (Mean = Median = Mode)\nHas Mean (µ) = 0 SD (σ) = 1\n\nMean ± 1SD (µ ± 1σ) covers 68% values\nMean ± 2SD (µ ± 2σ) covers 95% values\nMean ± 3SD (µ ± 3σ) covers 99% values\n\n- In a Normal distribution, 50% of values lie above the mean and 50% lie below the mean.\nMean is 265 days , SD = 15\nMean + 1 SD = 250, 280\nAs Mean + 1 SD covers 68% values.\nSo percentage of all pregnancies will last between 250 and 280 days is 68%.', 'role': 'assistant'}]