Year 12s: what will be the first way you research your future options? >>

S1 Normal distribution help

This question always confuses me, even though I can figure out most other normal distribution questions.

Mean = 0, standard deviation = 1
I need to find z when P(-z < Z < z) = 0.2206
What do I need to do to work this out? Any help is appreciated!

Reply 1

m4ths/maths247

Original post by skyluigi2

Have you sketched it?
Are you happy with the symmetry of the curve?
Can you use the tables?

Reply 2

skyluigi2

Original post by m4ths/maths247

Have you sketched it?
Are you happy with the symmetry of the curve?
Can you use the tables?

I've sketched it and understand the symmetry. I have the standard table for the mean/standard deviation this question uses... just can't figure out the method.

Reply 3

m4ths/maths247

Original post by skyluigi2

I've sketched it and understand the symmetry. I have the standard table for the mean/standard deviation this question uses... just can't figure out the method.

What would you say if I made the suggestion P(Z< z) = 0.1103 + 0.5 ?
Would I be right to make that comment or not?

(edited 10 years ago)

Reply 4

skyluigi2

Original post by m4ths/maths247

What would you say if I made the suggestion P(Z< z) = 0.1103 + 0.5 ?
Would I be right to make that comment or not?

Hmm... that sounds right. I could also split the question into two, couldn't I? So instead of P(-z < Z < z), I could have P(-z < Z < 0) + P(0 < Z < z)?
Having said that, I don't think I'd need to... I think I've worked it out and found that z = 0.28. Thanks for the help!