Final answer:
The incubation times that make up the middle 39% are 21 to 23 days.
Step-by-step explanation:
The mean incubation time for a fertilized egg is 22 days with a standard deviation of 1 day.
To find the incubation times that make up the middle 39%, we need to find the range of values that represent 39% of the total distribution.
We know that the mean is 22 days and the standard deviation is 1 day.
Since the distribution is bell-shaped and symmetric, we can use the empirical rule to estimate the range.
The empirical rule states that approximately 68% of the data falls within one standard deviation of the mean, 95% falls within two standard deviations, and 99.7% falls within three standard deviations.
Therefore, the middle 39% of the data would fall within approximately one standard deviation above and below the mean.
So the incubation times that make up the middle 39% would be from 21 to 23 days.