# Homework Question

#### eamon305

##### New Member
Hi, I have a homework question that I don't fully understand. It reads like this:

The mean weight of antarctic penguins found in a colony last year was 15.4 kg. In a sample of 35 penguins same time this year in the same colony the mean weight was 14.5kg. Assume the population standard deviation is 2.5kg. Find the 95% confidence interval for the population mean. Possible answers:
1. (13.77, 14.53),
2. (13.27, 15.43),
3. (12.37, 14.35),
4. (13.77, 15.43).
Is this a difference of two means question? Or something else?
Thank you any help would be much appreciated!

#### staassis

##### Active Member
It seems that the mean weight from the previous year is reported just to see if you can be led astray. Sometimes textbooks do that. They add extra information. And you are supposed to know that nothing has changed about the formula for calculating the correct answer.

Note that the sample size is not reported for the previous year. So the mean weight from the previous year is useless.

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#### eamon305

##### New Member
Okay i see what you mean. Thanks a million!

#### eamon305

##### New Member
On a side note, would i ise a z score or a t score to calculate this?

#### staassis

##### Active Member
Z-score since the standard deviation is communicated to you by God in unconditional fashion.