The midpoint of an interval is an average of the interval's lower and upper limits. To find it:

1. Add the lower limit to the upper limit.
2. Divide this sum by 2. The result is the midpoint.

Variance uses squares, whereas the standard deviation is expressed in the same units as the mean, so the latter is easier to interpret and use. However, you must calculate the variance to obtain the standard deviation.

Variance uses squared differences from the mean to prevent obtaining negative values or zero due to canceling out the terms. It also weighs outliers more heavily than data closer to the average, so the differences are more significant.