The mean of a data set is determined by calculating the sum of the values and dividing by the number of values in the data set.
The sum of the ages, in years, in the data set is 703, and the number of values in the data set is 12.
Thus, the mean of the ages, in years, of the first 12 United States presidents at the beginning of their terms is
.
The fraction
cannot be entered into the grid, so the decimal equivalent, rounded to the nearest tenth, is the correct answer.
This rounded decimal equivalent is 58.6.