HeroicPandas
Heroic!
- Joined
- Mar 8, 2012
- Messages
- 1,547
- Gender
- Male
- HSC
- 2013
1) Eight people are to be divided into 2 groups. What is the probability that there will be 4 in each group.
My go
NOTE:Some LaTeX error: 'm77' is 7C7
2) 6 humans, of whom A and B are two, arrange themselves at random in a row. What is the probability that there are at least 3 humans between A and B?
my go
For question 2, my explanation is:
For 3 between:
[A _ _ _ B] _
Deal with elements between A and B. A and B are gone, 4 are left, so choose 3 out of 4 (4C3) then times by 3! for their arrangements
Arrangements of individual elements (the grouped and single one) = 2!
A and B can switch places = 2
Therefore = 2 x 2! x 4C3 x 3!
For 4 between:
[A _ _ _ _ B]
Elements between A and B = 4C4 x 4!
A and B can switch = 2
Therefore = 2 x 4! x 4C4
what am i doing wrong??
I'd appreciate help with this (I am not good at this)
My go
NOTE:Some LaTeX error: 'm77' is 7C7
2) 6 humans, of whom A and B are two, arrange themselves at random in a row. What is the probability that there are at least 3 humans between A and B?
my go
For question 2, my explanation is:
For 3 between:
[A _ _ _ B] _
Deal with elements between A and B. A and B are gone, 4 are left, so choose 3 out of 4 (4C3) then times by 3! for their arrangements
Arrangements of individual elements (the grouped and single one) = 2!
A and B can switch places = 2
Therefore = 2 x 2! x 4C3 x 3!
For 4 between:
[A _ _ _ _ B]
Elements between A and B = 4C4 x 4!
A and B can switch = 2
Therefore = 2 x 4! x 4C4
what am i doing wrong??
I'd appreciate help with this (I am not good at this)
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