Alternative Suggested Solutions to Exam 2!

[decentxion]

Hey guys!

Looks like someone's beaten me to sending answers through to the admin, oh well!
Quite a few of my answers differed in explanation, however all the answers were identical. Here's a more "high-school" approach to the E2! Please note, Q4c) was not simplified, and the answer should be [2root2 - root6] units.

Here's a link to my solutions: http://docdro.id/9hDwOZI

Feel free to PM me with questions about the exam, otherwise please direct all other comments about the exam to the main topic!

[Deonyi]

I think 4bi is wrong; it should be 4-3ln(3) not 4-ln(3). This means your answer of 8-6ln(3) would make a bit more sense.

[bananabreadbelle]

For question (3g) wouldn't you need to multiply the standard deviation by the Z-score for a 95% C.I. in the formula?
Giving you (0.01 , 0.11)?

[Blueyneilo]

Perhaps 3f is not a "without replacement" type of question? It doesn't say anything about how many of the 100 sampled laptops did have a battery life below 3 hours (but you would expect exactly half of them to). Would each of the selected laptops just have 1/2 chance to have a battery life under 3 hours? I wonder if 25/198 and 1/8 will both be acceptable answers. Most of your other answers are reassuring. Thanks 

[exit]

Disagree with 3f. We are not given any prob other than there is a infinitely large population where to prob is 1/2. Can't see how it would be different if we were pick each computer one by one in comparison to 100 at a time where we have no idea how many of what is in it THEN testing one by one.

[decentxion]

I think 4bi is wrong; it should be 4-3ln(3) not 4-ln(3). This means your answer of 8-6ln(3) would make a bit more sense.

Yep sorry! Was rushing to get this done after work.

[decentxion]

For question (3g) wouldn't you need to multiply the standard deviation by the Z-score for a 95% C.I. in the formula?
Giving you (0.01 , 0.11)?

Yep my bad! Chuck in the 1.96 and it'll give you (0.01,0.11).

[decentxion]

Perhaps 3f is not a "without replacement" type of question? It doesn't say anything about how many of the 100 sampled laptops did have a battery life below 3 hours (but you would expect exactly half of them to). Would each of the selected laptops just have 1/2 chance to have a battery life under 3 hours? I wonder if 25/198 and 1/8 will both be acceptable answers. Most of your other answers are reassuring. Thanks 

Had a good think about this, and I agree. My original answer was 1/8 anyway, so I was tossing up between the 2 answers from the start. The sample size doesn't matter, since each individual laptop has a 50% chance of being under 3 hours, I agree completely.