While computing the mean of grouped data, we assume that the frequencies are :

1. evenly distributed over all the classes

2. centred at the class marks of the classes

3. centred at the upper limits of the classes

4. centred at the lower limits of the classes

If the mean of five observations x, x + 2, x + 4, x + 6 and x + 8 is 11, then the mean of first three observations is :

1. 9

2. 11

3. 13

4. none of these

The mean of 5 consecutive odd numbers of set A is 37. What will be the average of set B containing four consecutive even numbers if the smallest number of set B is 13 more than the greatest number of set A?

1. 53

2. 55

3. 57

4. 59

If the mean of four observations is 20 and when a constant c is added to each observation the mean becomes 22. The value of c is :

1. −2

2. 2

3. 4

4. 6