Finding the standard deviation and mean for x bar if you don't know x bar

Kufo

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Nov 25, 2022
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Q. A weights of cattle in a herd are normally distributed with mean 840 pounds and standard deviation of 30

a) one of these cattle is selected at random, and we let x = that cow's weight. Find P(X > or equal to 850)

Hopefully I did this one right. I plugged into NormalCDF (850, 9000, 840, 30) for 36.94% chance the cow weighs more than 850lbs.

Ok this is the one I need help on I just figured I'd ask if I did that question right.

B) A random sample of 30 of the cattle is selected, and the sample mean x bar is calculated. Find the mean and standard deviation for x bar.

I can't remember anywhere in our lectures where we went over this. But I thought I remembered that 30 is the break off limit for samples having a normal distribution. Am i correct in thinking that the mean and standard deviation is what was provided for me already since this sample size should represent a normal distribution?
 
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