# Two stats problems

• May 28th 2007, 01:06 PM
aargh27
Two stats problems
I have the key book but my answers aren't coming up the same so I know I am messing up somewhere. If you can help I'd be very thankful

a)
If the mean salary for high school teachers in the US is \$29,835 and the standard deviation is \$3000, find the probability that a teacher makes more than \$35,000.

So I first have to find the Z score, which would be = 35,000-29835 / 3000

Z= 1.72166

which = .4657 (around) after looking at a chart

and to find the probability above 35,000, I had .5000 - .4657 = .0341

b)
Houses in a certain neighborhood sell for an averae price of \$126,000 with a standard deviation of \$3,000. Find the Range for the middle 85% of houses in the neighborhood

Ack I found what I did wrong. I misread it as 95% and treated it as a confidence interval problem.
To find the correct answer, would I treat it as a Z score problem?
• May 28th 2007, 01:31 PM
CaptainBlack
Quote:

Originally Posted by aargh27
I have the key book but my answers aren't coming up the same so I know I am messing up somewhere. If you can help I'd be very thankful

a)
If the mean salary for high school teachers in the US is \$29,835 and the standard deviation is \$3000, find the probability that a teacher makes more than \$35,000.

So I first have to find the Z score, which would be = 35,000-29835 / 3000

Z= 1.72166

which = .4657 (around) after looking at a chart

and to find the probability above 35,000, I had .5000 - .4657 = .0341

I don't know what table you are using but mine gives:

P(Z<=1.72) = 0.9573,

so:

P(Z>1.72) = 1-0.9573 = 0.0427

Also this is all invalid without a statement to the effect that the distribution
of salaries is normal, or that you are assuming it so.

RonL
• May 28th 2007, 01:55 PM
aargh27
My table isn't exact so I estimated... and no, there is no statement about the the sales being normal but I am pretty sure I am ment to assume it, yes.