You are Here: Home >< Maths

# S2 - easy question? watch

1. I have a question from a solomon paper...maybe I am just being incredibly dumb, but I don't get the right answer to question 5)a)ii).
What I don't understand is why P(X>5) for probability 0.65, the same as P(x<5) for prob 0.35. ...Why is it not p(x<=5)?
Thank you.
Attached Images

2. For this question, it asks the probability of more than five, which is equal to 1-probability of it being less than or equal to five....the binomila tables show
P(x«X), so up to, and equal to, 5
3. This is hard to explain but:
My tables only go up to 0.5...so I can't get 0.65.
If that is not what you meant, and you meant to use 0.35 as a probability, then for some reason the answer is not 1- P(X<=5).
Also for the sake of this argument lets assume that we have to use the tables.
4. aha, I see the question, right, the probability of more than 5 being decreased in price is the same as the probability of less than or equal to 5 increasing in price, which uses the 0.35 probabilty (this is because the overall sample is 10) ....so is .9051 the correct answer?
5. The actual answer is 1-P(X<=4) with a probability of 0.35.
I'm glad it's not just me that is getting confused by this...
6. It is p(x<=4) yes, my bad lol, forgot 10 counts as zero >.<, but 1-probability? ..that I am confused about..
7. whoops, you are right not 1-probability...but is there any chance you could explain what you mean by 10 counts as zero?
8. Increasing in price ........Decreasing in price
.........0...................... .........10.................
.........1...................... ..........9.................
.........2...................... ..........8................
.........3...................... ..........7................
.........4...................... ..........6................
.........5...................... ..........5.................
.........6...................... ..........4................
.........7...................... ..........3...................
.........8...................... ..........2................
.........9...................... ..........1.................
.........10..................... ..........0...............

So 10 of them increasing price is the same as 0 of them decreasing price, and vice versa...so as you can see, the probability of more than 5 decreasing in price is the same as 4 or less increasing in price
9. ah ok, much clearer thank you.

### Related university courses

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: June 21, 2005
The home of Results and Clearing

### 1,021

people online now

### 1,567,000

students helped last year
Today on TSR

### University open days

1. Keele University
Sun, 19 Aug '18
2. University of Melbourne
Sun, 19 Aug '18
3. Sheffield Hallam University
Tue, 21 Aug '18
Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams