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# My uphill battle with Statistics watch

1. (Original post by ServantOfMorgoth)
Guys I flopped my statistics incourse test
Hard luck. Post more questions here.
2. (Original post by Gregorius)
Hard luck. Post more questions here.
If X is the random variable "number of fours obtained when 2 dice are thrown" what is the probability that 0 fours are obtained and only 2 fours are obtained?

I can assure you that this is only part of a question and I'm not asking anyone to do my work whole sale for me.

Zacken
3. (Original post by ServantOfMorgoth)
If X is the random variable "number of fours obtained when 2 dice are thrown" what is the probability that 0 fours are obtained and only 2 fours are obtained?

I can assure you that this is only part of a question and I'm not asking anyone to do my work whole sale for me.

Zacken
What's the probability that a "not 4" is obtained on the first die? And what about on the second die? For both dies to have a "not 4" you need to multiply those two probabilities together because you want P(not 4 and then not 4 again).
4. (Original post by Zacken)
What's the probability that a "not 4" is obtained on the first die? And what about on the second die? For both dies to have a "not 4" you need to multiply those two probabilities together because you want P(not 4 and then not 4 again).
11/36 × 11/36 ?

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5. (Original post by ServantOfMorgoth)
11/36 × 11/36 ?

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Well, not quite. The probability that a not 6 occurs on the first die is 5/6. Same on the second.
6. (Original post by Zacken)
Well, not quite. The probability that a not 6 occurs on the first die is 5/6. Same on the second.
And for the 2 fours is 1 - (5/6)^2 ?

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7. (Original post by ServantOfMorgoth)
And for the 2 fours is 1 - (5/6)^2 ?

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8. (Original post by Zacken)
Thanks

What about the 1? Is that 11/36?
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9. (Original post by ServantOfMorgoth)
And for the 2 fours is 1 - (5/6)^2 ?

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Oh dear, I'm not sure why I said yes to this. That's not correct.

Two fours means four on one go (1/6) and then four on the second go (1/6). So 1/6 * 1/6.
10. (Original post by High Stakes)
Remember.

AND rule is multiplication
I don't know why but whenever I see your profile picture I start to
as I really want to get a cute little baby husky.

11. (Original post by ServantOfMorgoth)
If X is the random variable "number of fours obtained when 2 dice are thrown" what is the probability that 0 fours are obtained and only 2 fours are obtained?
Zacken has already given some useful advice; let me suggest a simple (and surprisingly powerful) technique to complement the approach he's given. Instead of thinking in terms of probabilities, think in terms of counting.

So, when you have a problem like this, ask yourself, "can I list the possible outcomes in a consistent (and hopefully easy to think about) way?" Here we throw two dice; the first can come up 1 to 6, the second can come up 1 to 6. The set of possible outcomes can be displayed as a 6x6 two-dimensional grid: first throw along the top, second down the side. Each of the 36 cells here is equally likely, so to get the probabilities that you require, simply count the number of cells that meet the relevant criterion of the question and divide by 36.
12. (Original post by Gregorius)
Zacken has already given some useful advice; let me suggest a simple (and surprisingly powerful) technique to complement the approach he's given. Instead of thinking in terms of probabilities, think in terms of counting.

So, when you have a problem like this, ask yourself, "can I list the possible outcomes in a consistent (and hopefully easy to think about) way?" Here we throw two dice; the first can come up 1 to 6, the second can come up 1 to 6. The set of possible outcomes can be displayed as a 6x6 two-dimensional grid: first throw along the top, second down the side. Each of the 36 cells here is equally likely, so to get the probabilities that you require, simply count the number of cells that meet the relevant criterion of the question and divide by 36.

Oh I knew about the square but I didn't realise I had to divide by 36. I guess I was using it wrongly the whole time.

This is the entire question but I have no idea how to do part vi
13. (Original post by ServantOfMorgoth)

This is the entire question but I have no idea how to do part vi
You've worked out that Var[X] = 5/18, so you can work out . You know that . So which of the possible values of X lie between and ? You do part vii the same way...
14. CAn i assume ill be doomed if i have done only S1 at A levels ?
15. (Original post by Duke Glacia)
CAn i assume ill be doomed if i have done only S1 at A levels ?
No. At undergraduate level (in mathematics, anyway) we start teaching statistics properly, rather than the strange stuff that is done at A-level.

If you want to prepare yourself, think about drawing coloured balls from bags in various different ways; much of first year probability comes down to variations on this; then you start the interesting stuff.
16. (Original post by Gregorius)
No. At undergraduate level (in mathematics, anyway) we start teaching statistics properly, rather than the strange stuff that is done at A-level.
Statistics is the devil. Sadly, very important as a biologist.

What strange stuff?
17. (Original post by Kvothe the arcane)

What strange stuff?
Oh I exaggerate, but when I look at the probability and stats in A-level papers, I wonder why they bother. Probability and statistics are hard subjects, in that the techniques they use start where A-level runs out of steam. Would it not be better, I muse to myself, to concentrate on getting core stuff (algebra and calculus) more solid before venturing onwards and outwards. I have the same thoughts (but more so) about the Decision stuff at A-level.
18. (Original post by Gregorius)
I have the same thoughts (but more so) about the Decision stuff at A-level.
Seemingly, the higher ups agree with this. Decisions is being scrapped from the curriculum soon-ish.
19. (Original post by Gregorius)
Oh I exaggerate, but when I look at the probability and stats in A-level papers, I wonder why they bother. Probability and statistics are hard subjects, in that the techniques they use start where A-level runs out of steam. Would it not be better, I muse to myself, to concentrate on getting core stuff (algebra and calculus) more solid before venturing onwards and outwards. I have the same thoughts (but more so) about the Decision stuff at A-level.
I disagree I wished I had more experience with statistics at a level to get the basics down. I've had to start from square 1 and learn it in the equivalent of say S1 - S4 only 3 or so months. It's really hard.

I don't know anything about decision maths so my comment isn't about that.
20. (Original post by Zacken)
Seemingly, the higher ups agree with this. Decisions is being scrapped from the curriculum soon-ish.
Soon I will be in charge of everything

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