Hi all, It's rather long time I haven't dealt with maths. Now I have this problem. A man can shoot right on the target with the probability of success of p = 30%. The question is how many shots does he need to shoot to be 95% (P) successful. My idea is : Let n the number of shots needed. Then P = p^n+p^(n-1)*q+p^(n-2)*q^2....+p*q(n-1) where q=1-p. Am i right and if yes, how can I shorten the result? Thanks for any help.