The standard deviation for the combined assignment is 5 minutes.
To combine the standard deviations, we use:

With our information, we have:
The answer is: B
Explanation: 8 is fixed, not related to the number of marbles.
Answer:
Considering the Product and the Power rule of the Logarithms, they're both equivalent for x >0
Step-by-step explanation:
1) Considering the Product and the Power rule of the Logarithms:


2) Therefore we can say that:
