# Thread: Bi-nomial distribution - shorter method?

1. ## Bi-nomial distribution - shorter method?

I've noticed this question in an exam paper:

X is Bin(12,0.45)

a) Find $p(X\geq7)$
I could do this the long way which is to find $p(x=0)+p(x=1)+p(x=2)+p(x=3)+p(x=4)+p(x=5)+p(x=6)$ and then do one take away from this answer, but the question is two marks: surely there's a shorter method?

Edit:woops. mucked up the title...

2. Originally Posted by Quacky
I've noticed this question in an exam paper:

X is Bin(12,0.45)

a) Find $p(X\geq7)$
I could do this the long way which is to find $p(x=0)+p(x=1)+p(x=2)+p(x=3)+p(x=4)+p(x=5)+p(x=6)$ and then do one take away from this answer, but the question is two marks: surely there's a shorter method?

Edit:woops. mucked up the title...
Surely, you can use the binomial probability tables? As the Tables give probabilities for $P(X\leq x)$ than, $p(X\geq7)$ = $1- P(X\leq6)$

n= 12,
P = 0.45

3. Yeah, you're right! The thing is, I used the table in the textbook which doesn't have values for 12. I SHOULD have been using the formula booklet, which does