LC higher level 2016 P2 Q.9

[Lisa Kilmartin]

Hi there,

I wondered if I could ask a question regarding a (ii). 

when looking up 10% i.e. finding 0,9000 p value and then the z value for this,

why is z=1.28  (= -1.28 as 10%) taken as that is still in the 80 % range? 0.8997 , so this will not be in the lowest 10% , but in the 11th %, 10.03%

I am not seeing this right? Any help at all would be appreciated.

Many thanks,

Lisa

[Lucy de Faoite]

I think might just be a case of the 1.28 z-score being closer to 90% than 1.29.

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[Lisa Kilmartin]

Thanks Lucy, yes but in a 2020 Q. 8 there is a similar Q but they have used the zvalue  in the 75% (25%) region as was asked for so I just wondered if there is some rule that we can tell students as it seems to change which value is correct. 

Thanks for any help, 

All the best, Lisa

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[Lucy de Faoite]

If you for 0.67 as the z-score in 2020, you won't get a score that would be in the highest 25%? But with 0.68 will give you the score needed.

And with 2016, I know it's 0.03 out but you'll still be in the lowest 10%. Only reason I can think of. 

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[Trish Mulcahy]

Hi Lucy,

That’s my understanding too. You have to check the validity of your solution based on the specific situation of the question

Trish

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From: projec...@googlegroups.com <projec...@googlegroups.com> on behalf of Lucy de Faoite <whi...@tcd.ie>
Sent: Thursday, March 11, 2021 10:44:29 AM
To: projec...@googlegroups.com <projec...@googlegroups.com>
Subject: Re: [Project Maths Discussion] LC higher level 2016 P2 Q.9

 

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[Lisa Kilmartin]

Thanks for getting back to me, I appreciate that.

I think it is a difficult one to explain to students, how do they decide, based on the specific situation of the question?

Lisa

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