7. Use the formula S = n [ E ( f . x ) ] -[E( f . x)] to find standard deviation of the data n(n -1) summarized in the frequency distribution table below: Tar (mg) in Non- Frequency x(midpt) f . x f . x2 filtered Cigarettes 10- 14 1 15 - 19 2 20 -24 10 25 - 29 7 30 - 34 2 TOTAL n = >f Ef . x Efx [Hint: Complete the table and use the values from the table to evaluate the formula s; n = Efl a. S= " [ E( f . x ) ] -[E(f .x)] n(n -1)b. Also, find the mean. x= ((f . x) / Ef) c. Find the Coefficient of Variation