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AS maths binomial distribution question

A fair six-sided die is rolled six times. Which of the following is/are given by 6C2(1/6)^2(5/6)^4 ?
A: The probability of getting exactly one 2.
B: The probability of getting exactly two 1s.
C: The probability of getting exactly four 5s.
D: The probability of getting exactly five 4s.
E: The probability of getting exactly two scores less than 6.
F: The probability of getting exactly four scores greater than 1
Original post by jmyjmy
A fair six-sided die is rolled six times. Which of the following is/are given by 6C2(1/6)^2(5/6)^4 ?
A: The probability of getting exactly one 2.
B: The probability of getting exactly two 1s.
C: The probability of getting exactly four 5s.
D: The probability of getting exactly five 4s.
E: The probability of getting exactly two scores less than 6.
F: The probability of getting exactly four scores greater than 1

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Reply 2
Original post by jmyjmy
A fair six-sided die is rolled six times. Which of the following is/are given by 6C2(1/6)^2(5/6)^4 ?
A: The probability of getting exactly one 2.
B: The probability of getting exactly two 1s.
C: The probability of getting exactly four 5s.
D: The probability of getting exactly five 4s.
E: The probability of getting exactly two scores less than 6.
F: The probability of getting exactly four scores greater than 1

Its obviously from a binomial distribution, so any ideas?
Original post by mqb2766
Its obviously from a binomial distribution, so any ideas?

I can see that B would be 6C2(1/6)^2(5/6)^4, but I'm confused about E and F
Reply 4
Original post by jmyjmy
I can see that B would be 6C2(1/6)^2(5/6)^4, but I'm confused about E and F

Agree about that. For the last two, how would you write down the probabilities? Are they equivalent to any of A-D?
(edited 3 years ago)
Original post by mqb2766
Agree about that. For the last two, how would you write down the probabilities?

For E, would it be 6C2(5/6)^2(1/6)^4
And for F would it be 6C4(5/6)^4(1/6)^2
Reply 6
Original post by jmyjmy
For E, would it be 6C2(5/6)^2(1/6)^4
And for F would it be 6C4(5/6)^4(1/6)^2


And you know 6C2 = 6C4?
F must be the same as B, even if you don't understand probabilities?
Original post by mqb2766
Agree about that. For the last two, how would you write down the probabilities? Are they equivalent to any of A-D?

I don't think the last two would be equivalent to any of A-D, because the success probability is 1/6 for A to D, but this changes to 5/6 for E and F
Original post by mqb2766
And you know 6C2 = 6C4?
F must be the same as B, even if you don't understand probabilities?


OHHH I see.. thank you so much I understand now :smile:
Reply 9
Original post by jmyjmy
I don't think the last two would be equivalent to any of A-D, because the success probability is 1/6 for A to D, but this changes to 5/6 for E and F

Can you see which one E is equivalent to? It's not identical, but essentially the same.
Original post by mqb2766
Can you see which one E is equivalent to? It's not identical, but essentially the same.

Yes, is the probability of E equivalent to C?
Original post by jmyjmy
Yes, is the probability of E equivalent to C?

Yes. When using a binomial, you can go down the p or 1-p route, and note the nCr symmetry
nCr = nC(n-r)
Which is the symmetry in Pascal triangle.
Original post by mqb2766
Yes. When using a binomial, you can go down the p or 1-p route, and note the nCr symmetry
nCr = nC(n-r)
Which is the symmetry in Pascal triangle.

Since nCr = nC(n-r) is true, 6C2 = 6C4 = 15
Also, the row in Pascal's triangle when n = 6 is 1, 6, 15, 20, 15, 6, 1
Therefore it's 15 for the 2nd and 4th term in this row of Pascal's triangle!
Thanks so much for the help - I'm starting to love the statistics side of maths :smile:

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