Question

Heelllp, I am frustrated...
Use the normal distribution of SAT critical reading scores for which the mean is 513 and the standard deviation is 110. Assume the variable x is normally distributed.

a)What part of the SAT verbal scores is less than 650?

b) If 1000 SAT verbal scores are randomly selected, about how many would you expect to be greater than 575?


I am sooooooo, lost an confused. Please help!

Answer 1

your going to need a ztable or a stats calculator

Answer 2

\[z=\frac{x-\bar x}{sd}\]

Answer 3

I've downloaded a normal standard table.

Answer 4

\[z=\frac{650-513}{110}\]

Answer 5

For a, the z-score = (650 - 513)/110 = 1.245 for the z-score. Now, to the table.

Answer 6

this gives the zscore for x = 650

Answer 7

different tables express this in different ways

Answer 8

at any rate, you are over 50%

Answer 9

Should I round the 1.245 to 1.3?

Answer 10

that would be fine

Answer 11

if that value is less than .5 on yout table; than just add the .5

Answer 12

.8944 is what I see when I look at the normal standard table?
What do I to with that to get .5, that you you have

Answer 13

The area under the standard normal curve between z = 0 and z = 1.25 = .3944. Add .5 to that to get .8944 as the area under the curve below a z of 1.23.

89.44% of scores are less thatn 650

Answer 14

since that value is greater than .5; that tells me your table is measureing things from the left tail and not the mean itself

Answer 15

this same concept is applied to part b; but with the notion that you are aware of what the area it is your looking for is definedq

Answer 16

I'm using the table at this link:
http://www.mathsisfun.com/data/standard-normal-distribution-table.html

Answer 17

in the second part they expect you to knnow that you are looking for 1 - table value for the shaded region