The problem displayed involves determining the mean and standard deviation for a grouped frequency distribution of household temperature data. Here's how we can solve it step by step:

1. Class Midpoint Calculation:

   • For each class, the midpoint is calculated by taking the average of the lower and upper limits of each class.

   Midpoints provided:

   • $\text{Class } 61-64: \ 63.0$
   • $\text{Class } 65-67: \ 66.0$
   • $\text{Class } 68-69: \ 69.0$
   • $\text{Class } 70: \ 70.0$
   • $\text{Class } 71-72: \ 72.0$