Binomial question

#1
Hi,

I have attached a binomial question in excel (question & solution).

In part (e), the question asks for the P(between 5 and 15 inclusive)
The answer in cell B22 is:
0.9577 =BINOMDIST(15,B3,B4,1)-BINOMDIST(4,B3,B4,1)

Could you please explain why the solution refers to BINOMDIST(4,B3,B4,1) and not BINOMDIST(5,B3,B4,1)? i.e. why 4, not 5?

Thanks,
--Peter
 
#2
I couldn't open your file because I have a real old version of excel, but the last variable "1" makes the result cumulative.

So BINOMDIST(15,B3,B4,1) = P(X=0) + P(X=1) + ... + P(X=15)

And BINOMDIST(4,B3,B4,1) = P(X=0) + P(X=1) + ... + P(X=4)

So BINOMDIST(15,B3,B4,1)-BINOMDIST(4,B3,B4,1) = P(X=5) + P(X=6) + ... + P(X=15)