Math Is Fun Forum

Linderzzz

Member

Registered: 2010-04-20

Posts: 1

Normal Distribution

Hi everyone, I'm having trouble understanding how to approach the following problem:

The IQ of normal every day people is normally distributed with a mean of 100 and standard deviation of 16. On average, XX students are smarter than normal people; in fact the distribution of XX Students is normal with a mean of 112.3 and standard deviation 12.1. If you want to be in the XX smart club you need to have an IQ that is in the top 5% for XX students. What is that IQ?

Any input is greatly appreciated!

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Normal Distribution

Hi Linderzzz;

If I am reading your question right you only need the info about the XX people. They are normally distributed with a mean of 112.3 and a sd of 12.1. 1.96 sd's is the generally accepted number for 95% of the curve. But that is two tailed 2.5% on each side you need 5% on the right. So you need a z score of 1.645 for 90% of the curve, to have 5% on the right and 5% on the left.

Can you finish now?

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