Mean of 10 observations (numbers) is 20. If one number is included, the mean becomes 21, the included number is :

1. 431

2. 31

3. 231

4. 131

Mean of 20 observations (numbers) is 30. If one number is excluded, the mean of remaining numbers becomes 28. The excluded number is :

1. 532

2. 1132

3. 68

4. 572

If each observation of the data is decreased by 15; then the mean :

1. remains same

2. is increased by 15

3. is decreased by 15

4. is multiplied by 15

If the mean of x₁ and x₂ is 12.5 and mean of x₁, x₂ and x₃ is 16. The value of x₃ is :

1. 32

2. 3.5

3. 285

4. 23