A set of data is normally distributed with a mean of 75 and a standard deviation of 3. What percent of the data is in the interval 72–78?

The interval 72–78 is one standard deviation below and above the mean: 75 − 3 = 72 and 75 + 3 = 78. In a normal distribution, about 68.3% of the data lies within one standard deviation of the mean. So the correct choice is 68.3%.

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