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Statistics8 comments to Statistics |
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StatisticsShout here for any help on Stats… 8 comments to Statistics |
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Copyright © 2012 The Sydenham High School Mathematics Department Blog - All Rights Reserved |
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Hi Mrs Tibble,
I just have a quick question about the statistics homework. Im on ex3E, question 3a. To get x i was planning on multiplying 0.01 by 28 and then adding 50. But in the examples it only does the multiplying bit so am I know meant to add the 50? Thank you and I hope you are having a lovely half term
Hi Becky,
Standard deviation is about the spread of the values so coding by addition or subtraction of a constant won’t change the spread of the data. Multiplying or dividing however will alter the spread so only this has to be decoded.
This example is about range rather than s.d but I think it will give you the idea:
imagine our data set is {100, 110, 120, 130, 140}
the range is 140-100=40
now if we code the data using y=x-100
the coded values will be 0, 10, 20, 30, 40
and the range is 40-0=40
ie by shifting the values down the number line, the range hasn’t changed. By adding on 100 we’d be saying the range is now 140 which it clearly isn’t.
However, if we code the data using y=x/10
our coded data becomes 10, 11, 12, 13, 14
which has a range of 4.
This needs to be decoded by x by 10 to give 40 for the original data.
Look again at section 3.5 in the book and Example 9 making sure you read what’s in all the yellow boxes.
Have fun!!
Mrs T
Aaah thank you Mrs Tibble! I managed to work it out by looking at my notes in my book but then saw this and it explained it really well so I understand it completely. Thank you!
Im currently on question 7 of the stats you set me yesterday and am stuck on part B. Ive tried lots of different things but none of them seem to give me 0.15 which is the answer. Please help me Mrs Tibble and see im already back on the blog
Welcome back Becky
Have you got 1/12 for the intersection? (I’ve worked in fractions as it’s easier for this question)
That will give you the missing bit for D’s circle so you can start drawing the Venn diagram now. The intersection of C with not D is the crescent bit of C.
P(D)= 1/4 so P(not D) = 3/4
From the info given, P(C given not D) = 1/5
In terms of the diagram, this is the crescent of C divided by the not D space
therefore crescent/not D = 1/5 (or 0.2)
crescent/0.75 = 0.2
crescent = 0.75 x 0.2 = 0.15 or 3/20
With this you can now work out the outside region of the venn diagram and the rest of the questions should be OK using the right region of the diagram.
Hope that’s not too confusing as it’s hard to describe without a diagram!
Have fun
JT
Hi Mrs Tibble,
Yes I did that and then didn’t know what to do. Thank you, I understood in the end and have done it! Bet your glad to have me back on the blog…..:P ha ha x
Lol Becky. Isn’t it past your bedtime
that made me laugh so much miss! yes well its the weekend so im allowed to stay up late
Early night tonight though 