Official Edexcel S3 thread Wednesday 20 May 2015 Morning [6691]

I was getting you confused with ten of them, you names are similar.

I think I did some of your papers before, great website sir!

It will be far more useful if you do a degree with a high mathematical content.

Sorry many people confuse our names (I was here first)

Ah thanks, hmmn newb mistake on my part.


If anyone has access to the edexcel s3 pearson book, can you explain to me please on page 4 a) at the end of the question it goes from P(-1.44<Z<1.44) to 1.44 - - 1.44

Why does it do this and how is the final answer obtained.

Thanks.

I do not I am afraid

Apologies I should have quoted this separtely.

If anyone has access to the edexcel s3 pearson book, can you explain to me please on page 4 a) at the end of the question it goes from P(-1.44<Z<1.44) to 1.44 - - 1.44

Why does it do this and how is the final answer obtained.

Thanks.

Its a typo. They meant phi(1.44).
So,
P(-1.44<Z<1.44)=P(z<1.44)-(1-P(z<1.44))
= phi(1.44)-1+phi(1.44)
= 2phi(1.44) - 1

Thank you very much for the clear explanation.

May I ask you,

I get P(z<1.44) - (1- P(z<1.44)
0.9251 - (1-0,9251)
=0.9251-0.0749
=0.8502.

Can I ask do we leave answers for z values to 3 or 4 d.p.

The safe answer would be at least 3d.p if it isn't specified.

which paper lol?

Crap

I thought I was in the FP1 thread

tooooo many threads!

Last last question, do we have to use phi notation or we can just use the P( x < z) format and then just sub in the phi values as we go.


which paper lol?

I don't think they even expect us to use the phi notation. Use whatever notation suits you. It won't cost you marks.

Thank you.

Could someone have a look at Q3 on June 2010 and explain how you do part a? It's only two marks and seems incredibly simple but I can't remember what to do in that situation and the mark scheme isn't helpful in explaining why they do that

We have X - N(w, 0.5^2)

We are interested in P(W - 0.6 < X < W + 0.6)

But, and if you don't know why this is drawing a diagram of the areas under the normal represented by this probability would help,

This is the same as P(X < W + 0.6) - P(X < W - 0.6)

Now converting into z, for w + 0.6 we have (w + 0.6 - w)/0.5 and (w - 0.6 -w)/0.5

Giving 1.2 and - 1.2 respectively

So we have P(Z < 1.2) - P(Z < -1.2)

But, and again a diagram will illustrate this, P(Z < -1.2) = 1 - P(Z < 1.2)

So we require, rearranging, 2P(Z < 1.2) - 1

And the table does the rest