ok let's say: 15 18 21 23 27 30 37
the range is 37-15,
but how can i solve the variance??
First find the mean, then the variance is the mean of the squares of the differences between the data and the mean.
That gives the sample variance, if you want the unbiased estimator of the population variance use 6 rather than 7 in the last calculation.
All this is in your notes and/or text book.
RonL