S2 - can you explain something to me...

Watch
This discussion is closed.
RussianDude
Badges: 0
#1
Report Thread starter 15 years ago
#1
P(X≥4)=1-P(X≤3)
i cant understand this,
P(X≥4)=1-P(X≤4) makes more sense to me
cos if we draw the graph, where area under the graph = probability=1, and mark the region X≥4, i dont see how its possible to get X≥4 by 1-(X≤3)
0
Adil Bhai
Badges: 0
Rep:
?
#2
Report 15 years ago
#2
Basically its cos binomial distribution is discrete not continuous so you have to use consecutive integers.....i think

can anyone else confirm?
0
davedave
Badges: 0
Rep:
?
#3
Report 15 years ago
#3
P(X≥3) = P(X=3) + P(X=4) + P(X=5) etc

P(X≤3) = P(X=0) + P(X=1) + P(X=2) + P(X=3)

They would both include X=3, so it's P(X≤2).

Although I find it easier to look at as P(X≥3) = 1 - P(X<3)

and P(X<3) = P(X≤2) for discrete distributions.

Dunno why and maybe it's just me prefers to think of it like that
0
Trinity Blume
Badges: 0
Rep:
?
#4
Report 15 years ago
#4
(Original post by Adil Bhai)
Basically its cos binomial distribution is discrete not continuous so you have to use consecutive integers.....i think

can anyone else confirm?
Yes thats true. If you're using integers then what you say is true; whereas with continuous data the 2nd equation is correct.
0
Jonny W
Badges: 8
Rep:
?
#5
Report 15 years ago
#5
P(X >= 4) = 1 - P(X < 4) is always true, because exactly one of the events {X >= 4} and {X < 4} must occur.

If X is integer-valued then P(X < 4) = P(X <=3) so P(X >= 4) = 1 - P(X <= 3).
0
kimoni
Badges: 0
Rep:
?
#6
Report 15 years ago
#6
(Original post by RussianDude)
P(X≥4)=1-P(X≤3)
i cant understand this,
P(X≥4)=1-P(X≤4) makes more sense to me
cos if we draw the graph, where area under the graph = probability=1, and mark the region X≥4, i dont see how its possible to get X≥4 by 1-(X≤3)
The distribution is discrete, not continuous.
Ok, think about it this way. below there are 10 dots, labelled 1 to 10, they represent a probability distribution, so their sum is 1.

1 2 3 4 5 6 7 8 9 10
o o o o o o o o o o


P(X≥5) are the numbers 5 to 10, right? This is also the same as 1 (i.e. everything) - P(X≤4)

So, in essence P(X≥x) = 1 - P(X≤x-1)
0
RussianDude
Badges: 0
#7
Report Thread starter 15 years ago
#7
thanks guys, now i get it
0
X
new posts
Back
to top
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

If you do not get the A-level grades you want this summer, what is your likely next step?

Take autumn exams (19)
42.22%
Take exams next summer (11)
24.44%
Change uni choice through clearing (10)
22.22%
Apply to uni next year instead (4)
8.89%
I'm not applying to university (1)
2.22%

Watched Threads

View All
Latest
My Feed