diff --git a/src/content/questions/comp2804/2022-winter-final/15/solution.md b/src/content/questions/comp2804/2022-winter-final/15/solution.md index 90a4c709..60f2f5dd 100644 --- a/src/content/questions/comp2804/2022-winter-final/15/solution.md +++ b/src/content/questions/comp2804/2022-winter-final/15/solution.md @@ -1,63 +1,17 @@ -Warning: I don't know but I can try - - - -There's no way this is the actual way to do the question, right? This is bullshit. I am LITERALLY losing my sanity +Here the thing is easy but tricky: + +For simplicity lets take a1 a2 and a3 are our permutations of set {1,2,3} + +so Pr(A=a1>a2) = 1/2 because swapping the values of the variables a1 and a2 will make the sign turn to > and violating the constraints. so we can swap in 2! ways and for all ways the signs will change except 1 way. ie : a1 > a2. + +under same logic we can say for Pr(B=a2>a3) = 1/2. + +Similarly for Pr(A intersect B ) = 1/3! = 1/6. because under only 1 condition a1>a2>a3 and swapping there values will lead to something else compared to the condition we want. + +so we can see Pr(A intersect B) < Pr(A) * Pr(B) + +what for the big numbers now ? like n = 100 or 200 instead of 3? + +actually n doesnt put an affect here because permutation is something know as a unform distributions. + +So irrespective of the value of n for a subset of k it will always be 1/k! as the probability to get a specific sign sequence.