Simple Binomial Distribution Question? Watch

gorgeousguy
Badges: 7
Rep:
?
#1
Report Thread starter 12 years ago
#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
reply
Aired
Badges: 1
Rep:
?
#2
Report 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
reply
El Matematico
Badges: 0
Rep:
?
#3
Report 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
reply
gorgeousguy
Badges: 7
Rep:
?
#4
Report Thread starter 12 years ago
#4
Ok thnaks seems quite simple now. Thanks.
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

University open days

  • Cranfield University
    Cranfield Forensic MSc Programme Open Day Postgraduate
    Thu, 25 Apr '19
  • University of the Arts London
    Open day: MA Footwear and MA Fashion Artefact Postgraduate
    Thu, 25 Apr '19
  • Cardiff Metropolitan University
    Undergraduate Open Day - Llandaff Campus Undergraduate
    Sat, 27 Apr '19

Have you registered to vote?

Yes! (266)
38.61%
No - but I will (46)
6.68%
No - I don't want to (51)
7.4%
No - I can't vote (<18, not in UK, etc) (326)
47.31%

Watched Threads

View All
Latest
My Feed