
Tennis probability
I got a question about probability.....
The probability that a tennis set will go to a tiebreaker is 14%. In 80 randomly selected tennis sets, what is the mean and std dev. of the number of tie breakers?
a) mean: 10.4; std dev: 3.1
b) mean: 10.4; std dev: 3.35
c) mean: 11.2; std dev: 3.10
d) mean: 11.2; std dev 3.35
Thanks everybody

We will assume each game is independent and that the probability of a tie is fixed for every game. Then this situation follows a binomial distribution.
Let X be the number of games with a tie: then $\displaystyle X\,$~$\displaystyle \,\text{Binomial}\,(80, 0.14)$
For a binomial distribution,
$\displaystyle E(X) = np = 80 \times 0.14$
and
$\displaystyle \sigma_X = \sqrt{np(1p)} = \sqrt{80 \times 0.14 \times 0.86}$

Thanks for your reply, It helped me alot....I'm kinda started to get some concept.....