You are Here: Home >< Maths

S2 - Finding a critical region

1. im just about there, but i always seem to be one off of what the answer should be. for example:

The probability of Brand A lotion curing a particular skin complaint it 0.35. Brand B is said to improve the cure rate. Brand B was tested on 20 people, and 10 people were cured of the problem. Show Brand B isnt significant at 0.05, and how many people out of 20 would be needed to be cured so the results are significant to 0.05?
This means

H0: p=0.35
H1: p>0.35

X~B(20,0.35)

P(X≥10) = 1-P(X≤9) = 1-0.8782 = 0.1218. >0.05 therefore not significant.

P(X≥c) ≤ 0.05

1-P(X≤c-1) ≤ 0.05

P(X≤c-1) ≥ 0.95

now from the table,
P(X=10) = 0.9468
P(X=11) = 0.9804

therefore c-1=11 and c=12

but...the answer says its 11, not 12. what have i done wrong?
2. I can't find anything wrong with your working.
Where was the question from?
The only thing I can think of is that they might have rounded 0.9468 to 0.95, but it's very unlikely.
3. I can't see anything wrong with your working either. Where did you get this question from, is from the book or an exam paper?
4. nope, nothing wrong with your answer, think the book is wrong on this one, i hate it when this happens cuz then you keep thinking youve made the mistake and keep goin over an ovr tryin to find something that isnt there.
5. it was from my Heinemann S2 textbook. i seem to get them wrong in past papers by about 1 like i said, so i went back to my textbook and started doing lots of the same type of question.

im gonna keep practicing them anyway, but its good news that i did it right and it is the answer that is wrong.

Register

Thanks for posting! You just need to create an account in order to submit the post
1. this can't be left blank
2. this can't be left blank
3. this can't be left blank

6 characters or longer with both numbers and letters is safer

4. this can't be left empty
1. Oops, you need to agree to our Ts&Cs to register

Updated: June 4, 2007
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:
Today on TSR

Help!

Will Oxford nullify my offer?

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

Chat with other maths applicants