Statistics Formulas & Basic Concepts Statistic formulas for class 8th, 9th, 10th, Calculation of mean, mode, median, mean deviation about mean & median, standard deviation, variance. Statistics For Class 10 MEAN FOR UNGROUPED DATA \[Mean=\frac{Sum \; of \; all \; observations}{Number\; of \; observations}\] \[Mean\left ( \overline{X} \right )=\frac{\sum x_{i}}{n}\] MEAN FOR A GROUPED DATA There are three methods for this 1) DIRECT METHOD \[Mean\left ( \overline{X} \right )=\frac{\sum f_{i}x_{i}}{\sum f_{i}}\; \; or\; \; \; \; \frac{\sum f_{i}x_{i}}{n}\] \[Where:\; \; x_{i} = Mid \; values,\; \; x_{i} = \frac{Lower\: limit+Upper\: limit}{2}\] \[\sum f_{i} = sum \; of\; all \; frequencies\] Table for finding Mean by Direct Method C-I \[x_{i}\] \[f_{i}\] \[f_{i}x_{i}\] - - - - - - - - - - - - - - - - - - - -