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Friday, March 24, 2006 


One class today, last one before Spring Break!
We did practice problems on the board:

The weights of babies born at HSC average 8 lbs. 1 oz. (There are 16 oz in 1 lbs.) with a standard deviation of 12 oz.

a) Find the percentage of babies with a birth weight between 7 lbs. and 9 lbs.

To find the mean:

We convert the 1 oz. to lbs. : 1/16=.0625 So the mean is 8.0625 lbs. and we store it in M.

To find the standard deviation:
Again convert to lbs. : 12/16=.75 So the standard deviation is .75 lbs. and we store it in S.

Now we use our calculator:
ShadeNorm(7,9,M,S) = 81.6% of babies are between 7 lbs. and 9 lbs.
*normalcdf(7,9,M,S) does the same thing but just doesn't show the graph*
*It has to be in this order - low, high, mean, standard deviation*

b)Find the weight, w, such that the percentage of babies with a birth weight greater than w is 60%.

Since it's using a percentage, we use InvNorm. This means if we use the inverse of 60%, which is 40% we'll get our answer.
On the Calculator: InvNorm(.4,M,S) = 7.87 lbs.

c)Find the weight, w, such that the percentage of babies with a birth weight less than w is 25%. In this question we also use InvNorm but since it wants 25% and less, we just use .25. On the Calculator: InvNorm(.25,M,S) = 7.55 lbs.

A College aptitude test is scaled so tha
t its scores approximate a normal distribution with a mean of 500 and a standard deviation of 100.

a)Find the probability that a student selected at random will score 800 or more points.

Mr. K showed us another way to figure this out:

On the calculater we adjusted the windows:



*You have to play with the y min and max to get a good graph*

Then after adjusting the windows we go ShadeNorm(800,1000,500,100) and we get .135%

You also get the same answer if you get the z-score and go ShadeNorm(z,5)

b)Find the score, x, such that 76% of the students have a score: i) less than x ii) more than x

i) less than x

Again using inverse norm.
On calculator: InvNorm(.76) and store in z.
We need to find x, so our formula is :
z * σ + µ
=z*100+500 = 570.6

ii)greater than x
Now we use the inverse of 76% which is 24%.

On the calculator: InvNorm(.24) and store in z

same formula as above,
z * σ + µ = z*100+500 = 429.4

After these problems Mr. K started to show us binompdf.
So our example was fliping 10 coins:
First off you edit your list so in list one it goes from 0 - 10.
Then put up binompdf(10,.5) - 10 is the number of tries, .5 is the probability, and store in L2.
Now look at your list and it'll show you the probability of getting 0 heads, 1 heads, 2 heads, etc. to 10.
To graph this we turn our stat plot on, choose the histogram, xlist: L1, and Freq: L2.
Window settings:

And that was all the time we had for, he'll explain all the things we can do with this stuff when we come back.

Homework for spring break:
-make a delicious account
-make sure ALL homework assignments are completed, all the way to chapter 3.4
-p.345 review the utlilities about the calculator numbers 25-30

That's it I think, have a nice spring break!

Andrew for the next scribe.

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