fruit wrote:
jeeteshsingh wrote:
tarek99 wrote:
VVVVN.... V represent voted... and N represent Not Voted.
Therefore % = .9 * .9 * .9 * .9 * .1 x 5!/4! x100 = 32.8% = B
Is there any general formula?
I can't get for what do you do 5!/4!
If the probability of a certain event is \(p\), then the probability of it occurring \(k\) times in \(n\)-time sequence is: \(P = C^k_n*p^k*(1-p)^{n-k}\)
In our case:
n=5
k=4
p=0.9
So, \(P = C^k_n*p^k*(1-p)^{n-k}=C^4_5*0.9^4*0.1\)
OR: probability of scenario V-V-V-V-N is \(0.9^4*0.1\), but V-V-V-V-N can occur in different ways:
V-V-V-V-N - first four voted and fifth didn't;
N-V-V-V-V - first didn't vote and last four did;
V-N-V-V-V first voted, second didn't and last three did;
...
Certain # of combinations. How many combinations are there? Basically we are looking at # of permutations of five letters V-V-V-V-N, which is 5!/4!.
Hence \(P=\frac{5!}{4!}*0.9^4*0.1\).
Also you can check Probability chapter of Math Book for more (link in my signature).
Hi -just out of interest on this - what would be your best strategy for actually calculating the final percentage from the numbers given. Like how would you best do the difficult calculation or estimate the answer without wasting lots of time? Many thanks