In a normal distribution 31% of the items are under 45 and 8% are over 64. Find the mean and S.D. of the distribution.

I need some help on the above number. Thanx.

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- February 3rd 2009, 04:46 AMokellonormal distribution -help!
In a normal distribution 31% of the items are under 45 and 8% are over 64. Find the mean and S.D. of the distribution.

I need some help on the above number. Thanx. - February 3rd 2009, 04:56 AMmr fantastic
.

Find the value of such that .

From it follows that .

Substitute your value of to get equation (1) with the unknowns and .

.

Find the value of such that .

From it follows that .

Substitute your value of to get equation (2) with the unknowns and .

Solve equations (1) and (2) simultaneously. - February 3rd 2009, 09:20 AMokellonormal distribution - help!
Hi Mr. Fantastic, thanx.

I got http://www.mathhelpforum.com/math-he...3c147d21-1.gif asand http://www.mathhelpforum.com/math-he...88de1d0a-1.gif as**-82.6**using a calculator.**70.6**

Kindly confirm. Thanks once again.

Regards,

Okello - February 3rd 2009, 11:42 AMmr fantastic
- February 6th 2009, 04:00 AMokellonormal distribution - help!
Hi Mr. Fantastic,

I made http://www.mathhelpforum.com/math-he...48f3713a-1.gif = 0.31 ..............(i)

and http://www.mathhelpforum.com/math-he...dacbc5e0-1.gif =0.08 ...................(ii)

implying that

0.31http://www.mathhelpforum.com/math-he...3c147d21-1.gif + http://www.mathhelpforum.com/math-he...88de1d0a-1.gif = 45 -----iii

0.08http://www.mathhelpforum.com/math-he...3c147d21-1.gif + http://www.mathhelpforum.com/math-he...88de1d0a-1.gif = 64 ------iv

And used calc to find 2 unknowns. And I got http://www.mathhelpforum.com/math-he...3c147d21-1.gif asand http://www.mathhelpforum.com/math-he...88de1d0a-1.gif as**-82.6**using a calculator.**70.6**

Await for your response.

Thanks - February 6th 2009, 04:11 AMmr fantastic
- February 15th 2009, 07:10 PMmatheagle
- February 16th 2009, 02:19 AMokellonormal distribution - help!
Hi Matheagle,

Have you calculated it?. What answer did you get?

Regards, - February 16th 2009, 02:28 AMmr fantastic
- February 16th 2009, 05:27 PMmatheagle
I'm going to put a similar problem on my exam next week.