HomeWork is way too hard this week...another q

Hi guys

Gradually I'm working through my stats homework question by question but they seem to just be getting harder. The question I have below, I don't even know where to start...can anyone give me so,e advice as to what I should be looking at?

"The aptitude test scores of applicants to a university graduate program are normally distributed with mean 500 and standard deviation 60. If the university wishes to set the cut-off score for grad programs so that only the top 10 % of applicants qualify for admission, what is the required cut of score? What percentage of applicants have test scores within two standard deviations of the mean?"

So far, all I have come up with is
10 % of 500 is 50
2 SD from the mean is 380 & 620
Square root of 60 is 7.74 ( does that mean 7.74 is the variance?)


And that really is all I have. I don't know where to go with this or how to figure it out, if anyone can give me some advice or hints on how to figure this question out, it really would be appreciated

The variance is the square of the standard deviation, not the square root.
How many standard deviuations above the mean will cut off 10%?

The variance is the square of the standard deviation, not the square root.
How many standard deviuations above the mean will cut off 10%?

I havent ent progressed much but can anyone tell me if any of these ideas arson the right track:

500 is the mean so 2 standard deviations from the mean account for 95%. ( answer to 2nd question)

3 sd from the mean account for 99% so the highest number within the spread should be 680 and the lowest 320.

the highest 10% have to score over 568 and between 680.

am I getting closer?

Not really.
1.282 standard deviations above the mean cuts off the top 10%.
where did you get 568 from?

Thanks

Lol to be honest i am trying everything at the moment.

3sd from the mean accounts for 99% = 680 if sd is 60.

10% of 680 is 68

500+68 = 568

How did you get the 10% answer?


Posted from TSR Mobile

From the normal distriobution tables.

Is this S1 homework?

It's elementary statistics in 1st year undergrad.

Thanks guys

Can anyone give me some advice on how I figure out the answers for the question I posted? (Eg what I have to calculate) It seems I have a lot to learn but this question is so baffling

read posts 11 and 12

Ok thanks

S o in order to figure this question out, I must learn about z-scores and standard normal

you need to learn a methodology so some simpler books with examples will help you.

mmm thanks guys

looking at the z-score, it's not so hard to calculate. It's just x - mean / sd

however I can't see how that relates to the question I have for homework...

I can see how the empirical rule can fit in here somewhere but the z-score I can't see how.

im not asking for the answer but can someone please explain how this question is to be calculated, things to be thought of etc, am I looking at this question wrong?

The z-scores are a way of standardising the data so that you can use the tables. i.e. You can now look up that z score in the normal distribution table.