Which of the following assertions are $\text{CORRECT}$?
- $P$ : Adding $7$ to each entry in a list adds $7$ to the mean of the list
- $Q$ : Adding $7$ to each entry in a list adds $7$ to the standard deviation of the list
- $R$ : Doubling each entry in a list doubles the mean of the list
- $S$ : Doubling each entry in a list leaves the standard deviation of the list unchanged
- $\text{P, Q}$
- $\text{Q, R}$
- $\text{P, R}$
- $\text{R, S}$