UPSC NDA Math Model Paper 8

Given, A set of 5 values 3, 5, 7, 9, 11 has standard deviation σ.
Consider, the data 5, 7, 9, 11, 13
Here, each observation is increased by a constant 2,
we know that, if each observation is increased by a constant k, then the standard deviation is unchanged.
Hence, the standard deviation of 5 values 5, 7, 9, 11, 13 is σ