Days to Maturity for Short-Term Investments. Note that there are 40 observations

Answer may vary one of the possible solution is as follows:
Limit value grouping:
A grouping method in which each class is used to represents a possible range of values (class limits). Each range consists of smallest value as the lower limit of the class and largest value as the upper limit of the class.
The class limits are termed as limit value classes, and this grouping method is referred to be limit value grouping.
The most appropriate place for use this limit value grouping method is that the data to be whole number in nature with relatively more distinct observation to employ single value grouping.
Steps to find the classes for the data set:
Step 1:
Obtain the (approximated) number of class which is seven to fourteen is given in the information.
Step 2:
Calculate the class width by using the following formula:
${\displaystyle \text{class width}=\frac{\text{Maximum observation-Minimum observation}}{\text{Number of classes}}}$
The minimum value is 36 and maximum value is 99.
${\displaystyle \text{class width}=\frac{99-36}{7}}$
${\displaystyle =\frac{63}{7}}$
${\displaystyle =9}$
Thus, the class width is approximately equal to 9.
Step 3:
Obtain the lower class limit which is less than or equal to the minimum value of the data set.
Thus the choice of lower limit of the class is 35 which is less than that of 36 (minimum observation).
Step 4:
From the information given in table 2.6 of days to maturity for 40 short terms investment is started with class width of 10 then the first class limit will be less than 40 which is 35-44.
Thus the remaining classes for the data set are given below:
$\begin{array}{|c|}\hline \text{Days to maturity}\\ 35-44\\ 45-54\\ 55-64\\ 65-74\\ 75-84\\ 85-94\\ 95-104\\ 99\\ \hline\end{array}$