A grouped frequency distribution table with class intervals of equal size using 250 - 270 (270 not included in this interval) as one of the class intervals is constructed for the following data :

268, 220, 368, 258, 242, 310, 272, 342, 310, 290, 300, 320, 319, 304, 402, 318, 406, 292, 354, 278, 210, 240, 330, 316, 406, 215, 258, 236.

The frequency of class 310 - 330 is

1. 4

2. 5

3. 6

4. 7

The mean of x - 1, x + 1, x + 3 and x + 5 is

1. x + 1

2. x + 2

3. x + 3

4. x + 4

If the mean of x₁, x₂ is 7.5, and the mean of x₁, x₂, x₃ is 8, then the value of x₃ is

1. 9

2. 8

3. 7.5

4. 6

If each observation of the data is increased by 5, then their mean

1. remains the same

2. becomes 5 times the original mean

3. is decreased by 5

4. is increased by 5