# Math Help - stats-binomial distribution

1. ## stats-binomial distribution

the random variable x has a binomial distribution with n=6 and p=0.2

calculate P(X=6), I have tried this question several times and suspect it it not that difficult however I keep coming out with the wrong answer.

Is it 6choose6 x 0.2^6 x 0.8^0 ??

also how would I go about calculating

Given that Z~B(9,0.45) calculate P(Z=4 or 5)

Any help would be great thanks

2. the first answer is correct.

For the second: $P(Z = 4 \ \text{or}\ 5) = \binom{9}{4}(0.45)^{4}(0.55)^{5}$ $+ \binom{9}{5}(0.45)^{5}(0.55)^{4}$

3. Originally Posted by lra11
the random variable x has a binomial distribution with n=6 and p=0.2

calculate P(X=6), I have tried this question several times and suspect it it not that difficult however I keep coming out with the wrong answer.

Is it 6choose6 x 0.2^6 x 0.8^0 ?? Mr F says: Yes. And that obviously simplifies to 0.2^6 ......

also how would I go about calculating

Given that Z~B(9,0.45) calculate P(Z=4 or 5) Mr F says: Pr(Z = 4) + Pr(Z = 5). Plug the numbers into the usual formula to solve for each probability.

Any help would be great thanks
..

4. ## thanks

thanks- yes I had done the second part correctly, it was just a case of entering the sum into the calculator correctly.

thanks for the help