probability problem

[efraim224]

i know that in coin toss the chances for dropping to heads or tails is 0.5.
how can i canculate the probability of the coin toss to drop 8 time in a row heads in 127 tries?
and after that how can i canculate it(with the range of 127 tries) with 3 diffenent variables with 3 different probabilities?
is theere a formula?
thanks for your help and sorry for the bad english:)