In the following distribution, what is the modal class?
| Class | Frequency |
|---|---|
| 0-10 | 15 |
| 10-20 | 20 |
| 20-30 | 45 |
| 30-40 | 15 |
| 40-50 | 25 |
Let the Mean and Variance of five observations $ x_i $, $ i = 1, 2, 3, 4, 5 $ be 5 and 10 respectively. If three observations are $ x_1 = 1, x_2 = 3, x_3 = a $ and $ x_4 = 7, x_5 = b $ with $ a>b $, then the Variance of the observations $ n + x_n $ for $ n = 1, 2, 3, 4, 5 $ is
