What is the mean deviation from the mean of the numbers 10, 9, 21, 16, 24 ?

If the total number of observations is 20, $$\sum {x_i^{}} $$ = 1000 and $$\sum {x_i^2} $$ = 84000, then what is the variance of the distribution?

The mean of the series x₁, x₂, ........, x_n is $$\overline X $$. If x₂ is replaced by $$\lambda$$, then what is the new mean?

For the data 3, 5, 1, 6, 5, 9, 5, 2, 8, 6 the mean, median and mode are x, y and z, respectively. Which one of the following is correct?