This used binomial probability.Originally Posted by skhan
Over here you need all 5 not to. The probability of that not happening is 90% thus,
Originally Posted by skhan
Here you have 25 of them, thus you need to find,Originally Posted by skhan
This is probability of two events. First find between 3 and 6 which is,Originally Posted by skhan
And then probability exactly 4 which is,
Now multiply them to get,
CaptainBlack for the nice trick for combinations using LaTeX really helped.