STATISTICS DOUBT!!! PLZ REPLY ASAP!!!

[I Jimmy I]

Hello everyone!
Im having an AS reset this year and frankly forgot some basics.....

My doubt is Question 5(ii) of Oct/Nov 2006

Given,
Mean(meou)=?
Variance=root(21)

This is how I tried solving it,
1.P(X>10)=0.7389
2.1-phi( (10-meou) / root21)=0.7389
3.-phi(10-meou/root21)=0.7389-1
4.phi(10-meou/root21)=0.2611

After step4 I get confused on how to find z of 0.2611, whether to do phy^-1(0.2611) and make it -ve or what!
Someone plz solve this and then ill ask my doubt more clearly

[I Jimmy I]

My doubt was if given to find the phy^-1 of any probability below 0.5 then I should do 1-(x) and add a -ve sign infront of that value or not...?

[Arthur Bon Zavi]

My doubt was if given to find the phy^-1 of any probability below 0.5 then I should do 1-(x) and add a -ve sign infront of that value or not...?

Correct.

[Arthur Bon Zavi]

My doubt was if given to find the phy^-1 of any probability below 0.5 then I should do 1-(x) and add a -ve sign infront of that value or not...?

Yes add a negative value whenever you do this. This was the only doubt ? So the same you apply to the question in the paper you have posted.

[I Jimmy I]

Ye that was my only doubt

Other working is easy Just wanted to understand the concept! Anyways tyvm for confirming

[Arthur Bon Zavi]

Ye that was my only doubt

Other working is easy Just wanted to understand the concept! Anyways tyvm for confirming

Otherwise, you know what to do when value of z is positive or negative right ? Or make two equations and find mean and standard deviation.

[I Jimmy I]

I didnt quite understand what you meant. Could u give a question as an example plz?

[Arthur Bon Zavi]

I didnt quite understand what you meant. Could u give a question as an example plz?

Question 3 :

http://www.xtremepapers.me/CIE/International%20A%20And%20AS%20Level/9709%20-%20Mathematics/9709_s10_qp_61.pdf

Just try these types. They cover almost whole normal distribution and will make the topic easier for you.

[I Jimmy I]

Good news, I solved it with ease but that was definitely a first in using simultaneous equations in statistics or atleast the questions I covered.
Again TYVM for bringing this up

[I Jimmy I]

I got this other doubt in question 7(iii) of Oct/Nov 2006

The question is, Using a suitable approximation, calculate the probability that the number of small bands in the office pack is between 88 and 97 inclusive!

My doubt is how to write the inequality...? Whether to write it as  88<X<97     OR        88<=X<=97!

The reason Im asking is because this affects the c.c(continuity correction) while solving the question and therefore get a wrong answer

[Vin]

It says "inclusive" right. So greater than and equal to

[I Jimmy I]

So if the word inclusive wasn't there then I would go with 88<X<97 only?

[I Jimmy I]

And could someone confirm the following by simply writing "confirmed"

If given in B.D (Binomial Distribution) and changed to N.D(Normal Distribution) then use of C.C is necessary so.....
If it was 88<X<97 then it would become 88.5<X<96.5
However if it was 88<=X<=97 then it would become 87.5<=X<=97.5

Could some1 plz confirm whether the above is either correct or wrong! TYVM!

[SkyPilotage]

And could someone confirm the following by simply writing "confirmed"

If given in B.D (Binomial Distribution) and changed to N.D(Normal Distribution) then use of C.C is necessary so.....
If it was 88<X<97 then it would become 88.5<X<96.5
However if it was 88<=X<=97 then it would become 87.5<=X<=97.5

Could some1 plz confirm whether the above is either correct or wrong! TYVM!

Yup thts correct..

[I Jimmy I]

Tyvm