How do mean and standard deviation change after discarding outliers? **Sara measured the time in minutes between cars passing her camp near a desert road over a two hour period
The times she measured were 6, 6, 8, 9, 10, 11, 13, 13, 20, 24.
She calculated the mean and standard deviation for this set of data.
(She decided to reject the two outliers (20 and 24)
How do the new mean and standard deviation compare to her original ones?
A The mean and standard deviation both decrease.
B The mean and standard deviation both increase.
C The mean stays the same and the standard deviation decreases.
D The mean decreases and the standard deviation increases.
My answer is A ** 

Yes, you are correct: and for the reasons you give in your comments, too, [sort of for the mean (the divisor = sample size, will also decrease), but overall the mean will decrease].
As you state, as well, with respect to the standard deviation, the dispersion will certainly decrease without the values $20$ and $24$ removed. And the standard deviation will decrease as a result (the remaining values are more closely "lumped" together).
But it would also be good for you to confirm your answer by testing (computations). That way, you wouldn't need to even ask the question for verification! But it seems you have good enough intuition as to what mean and standard deviation represent, which is sufficient to answer the question as stated!
