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Binomial Probability

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Can somebody please help me with? If you can, would you explain and explain the steps to solving a problem. If needed i can give the problem out.

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Like tomat said, it would be easier to explain the given problem but here is some general information and examples:

- It deals with discrete distribution in which there is a fixed number of trials with only two possible outcomes (success and failure)

- each trial result is independent

For example:

Let say 220 out of 550 students studies Math SL. If you choose 25 students, what is the probability that 10 of them study Math SL?


( A ) P(Math SL) = 220/550 = 0.4

( B ) This means that the distribution, X ~ B is (25, 0.4)

( C ) Then when you calculate the bionomial probability using the formula [has put a picture]


Where P (X = r) is the function

r = (0, 1, 2, 3…sort of ‘x’)

n = sample (i.e ‘if you choose 25 students…)

n-r = failures

p = probability of success

q = probability of failure (1 – p)

calculation (once again a picture)


To calculate the C thing, you can use your calculator the 'nCr' option. I use TI and to access it I go to math - prb. It's the same one you use when calculating bionomial expansions.

Another way is to calculate through;

P (x = 10) = binompdf(25, 0.4 , 10) = 0,161 (again for TI, then Distr)

You can also do this in the 'reverse' part. Let say that the question is instead 'at least 10 of them of them study Math SL' then you need to do (again using word to write so its a picture):



I know this is all very confusing. It took me some time to understand it and basically - practising makes things easier to understand. I recommend that you read your math books again and again and try the questions :(

Edited by Afterglow

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