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1. Hi

Can anyone help with the following:

"The amount of fruit juice (in millimetres) in a grapefruit has a normal distribution with a mean of 90 and a variance of 100. The average amount of juice in a random sample of 25 grapefruit is A millimetres."

Find the probability that A differs from 90 by more than 4.

I have already calculated that N (90,4).

Thanks
2. (Original post by flutegirl02)
hi

can anyone help with the following:

"the amount of fruit juice (in millimetres) in a grapefruit has a normal distribution with a mean of 90 and a variance of 100. The average amount of juice in a random sample of 25 grapefruit is a millimetres."

find the probability that a differs from 90 by more than 4.

I have already calculated that n (90,4).

Thanks
p(|a-90| > 4) = 2p(a-90 > 4) = 2p(a > 94).
3. (Original post by Flutegirl02)
Hi

Can anyone help with the following:

"The amount of fruit juice (in millimetres) in a grapefruit has a normal distribution with a mean of 90 and a variance of 100. The average amount of juice in a random sample of 25 grapefruit is A millimetres."

Find the probability that A differs from 90 by more than 4.

I have already calculated that N (90,4).

Thanks
You know that , from the information, right? Now that you have a sample, you can also assume that by - it seems you've gotten that part! Now since you want to find , you can say that by finding and . This should make the rest simple from here!

EDIT: didn't see Zacken's comment
4. (Original post by Zacken)
p(|a-90| > 4) = 2p(a-90 > 4) = 2p(a > 94).
Thanks Zacken
5. (Original post by aymanzayedmannan)
You know that , from the information, right? Now that you have a sample, you can also assume that by - it seems you've gotten that part! Now since you want to find , you can say that by finding and . This should make the rest simple from here!

EDIT: didn't see Zacken's comment
Damn... I must be forgetting my S3 already. If it's a sample, wouldn't the mean stay the same ?
6. (Original post by Zacken)
Damn... I must be forgetting my S3 already. If it's a sample, wouldn't the mean stay the same ?
made a mistake Latexing doing maths using it makes things me so error prone. Your method is definitely right.
7. (Original post by aymanzayedmannan)
made a mistake Latexing doing maths using it makes things me so error prone. Your method is definitely right.
Anyways, mind if I pick your brain so I understand this properly? You've got two options/methods here, right?

You can either do like I did, or you can do:

and then look at ?
8. (Original post by Zacken)
Anyways, mind if I pick your brain so I understand this properly? You've got two options/methods here, right?

You can either do like I did, or you can do:

and then look at ?
Suppose if they asked you to find . I'd find and then standardise using the distribution I've found for previously.
9. (Original post by aymanzayedmannan)
Suppose if they asked you to find . I'd find and then standardise using the distribution I've found for previously.
Mind writing out the standardisation for me?
10. (Original post by Zacken)
Mind writing out the standardisation for me?
Does it help if i let so that ? You only need to find then, which I'm sure will look like familiar S1 stuff!
11. (Original post by aymanzayedmannan)
Does it help if i let so that ? You only need to find then, which I'm sure will look like familiar S1 stuff!
Ah, okay, thanks - yeah that does help. Is there any advantage over that method than the standard ?
12. (Original post by Zacken)
Ah, okay, thanks - yeah that does help. Is there any advantage over that method than the standard ?
I've picked this up from the textbook, Sean and Gregorius. I'm not sure if it has any advantages or not Possibly in following calculations/hypothesis tests? I'm glad the OP posted this, gives me a chance to see whether or not I actually understand S3.
13. (Original post by aymanzayedmannan)
I've picked this up from the textbook, Sean and Gregorius. I'm not sure if it has any advantages or not Possibly in following calculations/hypothesis tests? I'm glad the OP posted this, gives me a chance to see whether or not I actually understand S3.
Same. This is cool, I always used to use my method, but yours seems like it could come in handy. Might try practising it a bit.

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