Sample size (n) for sample mean w.r.t. ran vble X modelled as normally distributed

Hi there,
I've a handful of questions I'd like to put up here for perusal by the collective brains of the outfit. They all originate from the Edexcel Yr2 Stats and Mechs Practice book. Sadly, the book doesn't provide full solutions just the bare answer. I just cant seem to get the same answers they provide.

I wonder if anyone might be able to have a look at this question. Other questions to follow as different threads. I thought it would be more convenient to post the question, their answer, and my attempt as a utube video so please see if it makes sense. First 30 secs is their question followed by a slow scroll of what I've come up with.

https://youtu.be/4invlhX_V3s

Really appreciate it if any of you folks can keep me honest and set me straight.

It's possible you have an early (and error strewn) edition of this book. I've just looked at the online edition, and the answer for part (b) given there is 40. Note that you have to round UP not DOWN. If you're unsure why that's the case, try plugging the values 39 and 40 into the cumulative normal function of your calculator.

Hi there,
Could you advise on where I can obtain the updated answer sheet.

Hi there,
Also, can I ask, was my logic correct i.e. it is irrelevant what value of mean I choose as it has no impact w.r.t. the spread of the data?

No, sorry, I don't have a source for a copyright free version of the answer sheet.



Your logic is correct. In fact you don't even need to assume a value for mu, since you can just replace (Xbar - mu) by 1 or -1 as appropriate.