Question four asks about a coin toss. I have calculated an answer at least ten times using the binomial coefficients method but I cannot get it right.
I was hoping someone could help out.
The question asks: “Suppose that you flip a coin 13 times. What is the probability that you achieve at least 4 tails?”
I keep getting .0873 after dividing my binomial coefficient value by 2^{13}
I know this should be super easy but I just cannot get it.
Thank you!
I guess you’re trying to modify this Sage code that looks like so:
k = var('k')
sum(factorial(99)/(factorial(k)*factorial(99-k)*2**99), k,0,46)
Note that there are three 99s and you need to change all of them. There’s also a starting point of 0 for the sum and an ending point of 46. Finally, if you want a decimal approximation, you might try
k = var('k')
N(sum(factorial(99)/(factorial(k)*factorial(99-k)*2**99), k,0,46))
That N evaluates numerically.
It looks to me like you should be expecting a big number - like 0.9\ldots, since 4 is well under the mean.