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Edexcel S1 - 15th June, 2016 [Exam Discussion]

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The mean stayed the same, no? I checked it on my calculator


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Original post by iMacJack
The mean stayed the same, no? I checked it on my calculator


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You checked wrong then. It slightly decreases
Reply 1262
Avatar for cmrol
cmrol
5
Original post by bobbutitii
all of them


Probably not
Original post by tammymxx
Can anyonw walk me thru how they got their answer for Rach and Sarahs q


Sure, you use the brain i hope you have
Can somebody link me to an unofficial mark scheme please
Original post by cmrol
Probably not


probably yes
Original post by bobbutitii
all of them


Thank you very much for your lovely reply(!)


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Original post by bobbutitii
all of them


Nah sometimes you get dM1 marks, so a method mark
Original post by Pikki1234
Thank you very much for your lovely reply(!)


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anytime g xxxxxxx
Original post by googleit
You checked wrong then. It slightly decreases


thats what he is saying
Original post by Piers456
Nah sometimes you get dM1 marks, so a method mark


Yeah but for a worst case scenario, you assume 0 marks for now
Reply 1271
Avatar for cmrol
cmrol
5
Original post by bobbutitii
probably yes


I think that you would at least get one mark for correct method for generating a z value maybe one for using the table correctly.
Nope, the mean stayed the same. If you add something that is the mean, it's going to stay the same. Checking on the calculator only confirms the assumption.

The standard deviation does, however change. I believe it decreases as you are reducing the spread of data in this circumstance.

Original post by googleit
You checked wrong then. It slightly decreases
Guys if i got my value of k correct , however i messed up my width , therefore i got incorrect answer for height , even though my method is correct , how many marks will I lose out of 3 ?
Original post by googleit
The mean DECREASED guys, not stayed the same, we're dealing with classes here. The value of 3.43 will add one to the frequency of the 3-3.5 class. The way we work out the estimate is to multiply the midpoint of the class by the frequency. Hence, since the midpoint of this class is 3.25, which is lower than the mean, the mean decreases.
You could have also done the actual calculation to check, the mean decreased :smile:

EDIT: I'll explain this better. The mean before the added values was 3.43. Now there's an added value of 3.43. This adds one to the frequency of 3-3.5 class. In working out the value of the mean, you have to multiply mid point by frequency. Hence, you don't actually deal with 3.43 but rather 3.25, the mid point of the class. Since this value is less than 3.43 the mean decreases.
Try the calculation out for yourself and please amend the unofficial mark schemes.

I think people were just rounding, who knows
Original post by LukeB98
Nope, the mean stayed the same. If you add something that is the mean, it's going to stay the same. Checking on the calculator only confirms the assumption.

The standard deviation does, however change. I believe it decreases as you are reducing the spread of data in this circumstance.


sorry professor
Original post by Kawaii289
thats what he is saying


No he's not, the 'no' he said translates to 'isn't it'? He thinks the mean stayed the same
Original post by Pudge666
Guys if i got my value of k correct , however i messed up my width , therefore i got incorrect answer for height , even though my method is correct , how many marks will I lose out of 3 ?


are you an idiot?
Original post by googleit
No he's not, the 'no' he said translates to 'isn't it'? He thinks the mean stayed the same


oh sozzy
Original post by googleit
The mean DECREASED guys, not stayed the same, we're dealing with classes here. The value of 3.43 will add one to the frequency of the 3-3.5 class. The way we work out the estimate is to multiply the midpoint of the class by the frequency. Hence, since the midpoint of this class is 3.25, which is lower than the mean, the mean decreases.
You could have also done the actual calculation to check, the mean decreased :smile:

EDIT: I'll explain this better. The mean before the added values was 3.43. Now there's an added value of 3.43. This adds one to the frequency of 3-3.5 class. In working out the value of the mean, you have to multiply mid point by frequency. Hence, you don't actually deal with 3.43 but rather 3.25, the mid point of the class. Since this value is less than 3.43 the mean decreases.
Try the calculation out for yourself and please amend the unofficial mark schemes.


I know what you're saying, but I took it to mean that the 3.43 was factored in exactly as it is, not added to a class in the table. So I'm still going with the mean staying the same.

Either way, it seems a bit ambiguous?

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