Question

what is the probability the student does not get an A (less than 90) mean = 75 and standard deviation is 9

Answer 1

i wrote \[(90-75)/9=1.667\]

Answer 2

Are you using Zscores?

Answer 3

and then on the Z table it becomes .4525

Answer 4

yes

Answer 5

so then the answer is .0475 which is right

Answer 6

but then its asking me about the 99% percentile

Answer 7

which i am lost :/

Answer 8

The 99th percentile means the top 1%

Answer 9

ok

Answer 10

so how do i plug that in?

Answer 11

I'm not sure what you're doing with the 99th percentile.

I'm going to guess that you have to find where it begins.

Look at the z-tables, and find the Z-score that equates to 99% of the class being BELOW that point. Plug that Z-score into the equation for a Z score, and find the score needed.
\[Z = \frac{x-\mu}{\sigma}\]

Answer 12

2.33 i believe

Answer 13

Sounds about right

Answer 14

ok and then from there? im sorry

Answer 15

Use that Z score in the formula I posted, along with the mean and standard deviation. Solve for x. That's the score that begins the 99th percentile

Answer 16

95.97?

Answer 17

That's what I get :)

Answer 18

yay!!! thank you!

Answer 19

Make sure that's what the question was actually asking. You never actually told me the question. I just assumed that's what it was :P

Answer 20

you assumed right!