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4766 MEI S1 OCR May 20th 2015

Stats:nothing: all those equasions, this is one of the threads I see as being more active being that it's probably one of the harder exams. But we will get though it:work:

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Anyone got any resources for probability?? The only topic I really dont get!
Reply 2
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Original post by xoharrypotter
Anyone got any resources for probability?? The only topic I really dont get!

Any questions I can help with?
Reply 3
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Original post by Aph
Any questions I can help with?

How do you calculate probability from a histogram?
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Original post by Hody421
How do you calculate probability from a histogram?

You can't, well not directly... But prob is really unlikely to appear with a histogram
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Original post by Aph
You can't, well not directly... But prob is really unlikely to appear with a histogram

Oh sorry I didn't mean a histogram it was grouped data
The last two
groupeddata.png38.3KB
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Original post by Hody421
Oh sorry I didn't mean a histogram it was grouped data
The last two

Ahh, that looks like the binomial distribution and basic probability.
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Original post by Aph
Ahh, that looks like the binomial distribution and basic probability.

The second one looks more complicated

It's not simply the answer to part A + 3C1 x (12/50)^2 x (38/50)

But: 3C1 x 12/50 x 11/49 x(38/48) + answer to part A
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Original post by Hody421
The second one looks more complicated

It's not simply the answer to part A + 3C1 x (12/50)^2 x (38/50)

But: 3C1 x 12/50 x 11/49 x(38/48) + answer to part A

Ohh:facepalm: aye it isn't replacement is it, but are you ok with what you have to do?
Anyone know how to find the median of a histogram?:frown:
Urgh the stats exam next week

Everthing else but probability and permuation/combinations are okay for me :redface:

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Original post by thecalmmorning
Anyone know how to find the median of a histogram?:frown:

1) Find which group the median is in (remember to use (n+1)/2)
2) Find the position in its group ( Position in the group = Overall position - Number of positions below median group)
3) Find this position as a proportion of the median's group ( Position in the group/No. of values in the group)
4) Multiply the value from step 3 by the class width of the median group
5) Add the number to the median groups' lower class boundary, i.e if the median group is 10<x<20, Add the value to 10.
how do you find the critical region?
Critical region depends upon the significance level, whether it is two-tailed/one-tailed etc.
Original post by the boss.
how do you find the critical region?
I just did this question

For part iii I used 'If independent, P(A).P(B)=P(A∩B)', but the mark scheme says to use P(B|A) = P(B)


Would I get the marks? I would of thought the mark scheme would have made a note about other suitable methods being used...
Screen Shot 2015-05-17 at 21.38.07.png83.5KB
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Original post by AlexParmenter
I just did this question
For part iii I used 'If independent, P(A).P(B)=P(A∩B)', but the mark scheme says to use P(B|A) = P(B)
Would I get the marks? I would of thought the mark scheme would have made a note about other suitable methods being used...

You should do. But given P(A∩B) is calculated I wouldn't use it in case you got the answer wrong.
Who thinks there will be lots of probability this year?
5 A researcher is investigating whether people can identify whether a glass of water they are given is bottledwater or tap water. She suspects that people do no better than they would by guessing. Twenty people areselected at random; thirteen make a correct identification. She carries out a hypothesis test.

1.

(i) Explain why the null hypothesis should be p = 0.5, where p represents the probability that a randomlyselected person makes a correct identification. [2]

2.

(ii) Briefly explain why she uses an alternative hypothesis of p > 0.5. [1]

3.

(iii) Complete the test at the 5% significance level. [5]

hi guys, in part (iii) of this question, when finding the probability why is the answer P(X ≥13)=1–P(X ≤12)=1–0.8684=0.1316 and not simply that P(13)=0.9246? Because sometimes when doing hypothesis testing, you simply take the value for that number from the table and sometimes you have to do 1-(previous number)? i was hoping someone could please explain when to choose which one to do?
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Original post by the boss.
5 A researcher is investigating whether people can identify whether a glass of water they are given is bottledwater or tap water. She suspects that people do no better than they would by guessing. Twenty people areselected at random; thirteen make a correct identification. She carries out a hypothesis test.

1.

(i) Explain why the null hypothesis should be p = 0.5, where p represents the probability that a randomlyselected person makes a correct identification. [2]

2.

(ii) Briefly explain why she uses an alternative hypothesis of p > 0.5. [1]

3.

(iii) Complete the test at the 5% significance level. [5]

hi guys, in part (iii) of this question, when finding the probability why is the answer P(X ≥13)=1–P(X ≤12)=1–0.8684=0.1316 and not simply that P(13)=0.9246? Because sometimes when doing hypothesis testing, you simply take the value for that number from the table and sometimes you have to do 1-(previous number)? i was hoping someone could please explain when to choose which one to do?

Firstly P(13) =/= 0.9246.

And it depends on which tail you are looking at. If it's the probability is lower you take the value from the table. And the converse is true.
Original post by the boss.
5 A researcher is investigating whether people can identify whether a glass of water they are given is bottledwater or tap water. She suspects that people do no better than they would by guessing. Twenty people areselected at random; thirteen make a correct identification. She carries out a hypothesis test.

1.

(i) Explain why the null hypothesis should be p = 0.5, where p represents the probability that a randomlyselected person makes a correct identification. [2]

2.

(ii) Briefly explain why she uses an alternative hypothesis of p > 0.5. [1]

3.

(iii) Complete the test at the 5% significance level. [5]

hi guys, in part (iii) of this question, when finding the probability why is the answer P(X ≥13)=1–P(X ≤12)=1–0.8684=0.1316 and not simply that P(13)=0.9246? Because sometimes when doing hypothesis testing, you simply take the value for that number from the table and sometimes you have to do 1-(previous number)? i was hoping someone could please explain when to choose which one to do?


It depends on which way round the sign is, if you are working out p(X≤12) then you take the value straight from the table, if you are working out p(x≥12) then you would do 1-p(x≤11)

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