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
1. $\text{P, Q}$
2. $\text{Q, R}$
3. $\text{P, R}$
4. $\text{R, S}$