# Simple Binomial Distribution Question?Watch

#1
In a national survey of year 11, health researchers found that one third smoked cigarettes.

For a random sample of 25 pupils in year 11, find the probability, that:

B) there is more that one smoker?

I know this seems stupid but my method contradicts the mark scheme, but we get the same answer! In the mark scheme it says you set your ditribution like X-B(25,1/3), and I do the same. we both also say that to work it out you do "1 - p(x<2)".

However I then did this:

1 - (x=1) + (p=0)

However in the marksheme is says you:

1 - (x=1) - (p=0)

Who is right? Because I have the exam tommorow and am now confused.
0
12 years ago
#2
Well you have 1 - [P(x=1) + P(x=0)]

Which comes out at 1 - P(x=1) - P(x=0), so the markscheme is right.
0
12 years ago
#3
You need to do:

1 - P(x = 1) - P(x=0)

as the mark scheme says. But if you've done this:

1 - (P(x=1) + P(x=0))

Which are the same thing if you have the brackets as above.
0
#4
Ok thnaks seems quite simple now. Thanks.
0
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