Which of the following assertions are $\textbf{CORRECT}$?

• $P:$ Adding $7$ to each entry in a list adds $7$ to 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. $P, Q$
2. $Q, R$
3. $P, R$
4. $R, S$