A random number generator picks a number from 1 to 9 in a uniform manner.
Find the 90th percentile. (Round your answer to one decimal place.)
My set up is (k-9)(1/8)=0.90
why is this wrong

- anonymous

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- nincompoop

why did you use that "set up?"

- anonymous

in my book it says to use it

- anonymous

(base)(height)=0.90

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## More answers

- nincompoop

first, what do you know about percentile rank in your own words

- anonymous

isn't it like how many # were chosen...90%?

- nincompoop

so you're being asked for the number that ranks 90th percentile

- anonymous

right

- nincompoop

how would you look for that number

- anonymous

that's where I am getting confused because my set up is wrong?
would it be like 90%..of 9

- nincompoop

let us list your numbers

- nincompoop

is this how you have it set up?
1, 2, 3, 4, 5, 6, 7, 8, 9

- anonymous

okay yes

- nincompoop

there are two ways to get percentile ranks
one is:
\(\sf \huge \frac{B\times (0.5E)}{n} \times 100 \)
B: scores below x
E: number of scores equal x
n: total number
the other is:
\(\sf \huge \frac{B}{n} \times 100 \)

- nincompoop

if you're going to use the second one, the set up should be
\(\sf \large \frac{B}{9} \times 100 = 90 \)
remember that your B will be lower than the actual score you're looking for, but let us focus on properly solving for B first

- anonymous

so it would be 8.1?

- anonymous

8?

- anonymous

I thought it ment to keep the .1

- nincompoop

http://www.wolframalpha.com/input/?i=%28100*b%29%2F9+%3D+90

- nincompoop

round off is the same as estimation and you need to learn about place values.

- nincompoop

9.1 rounded off to 1 decimal means you focus on the first decimal
if it is between 0-4 then it becomes 0
if it is between 5-9 then you add 1 to the number that preceded it
9.1 = 9
9.5 = 10
9.67 = 10
etcetera etcetera

- nincompoop

let us check if our answer makes sense
http://www.wolframalpha.com/input/?i=8%2F9

- anonymous

I understand that, but the question says "Round your answer to one decimal place"
so therefore the answer would be like "9.4" keeping the 4

- nincompoop

8 out 9 makes almost 90%

- nincompoop

no

- anonymous

when I practice another problem with numbers 2-9 and asking for the 80th percentile, the answer is 7.6 ??

- anonymous

the .6 is kept

- nincompoop

http://www.mathsisfun.com/rounding-numbers.html

- nincompoop

you're right
you keep it

- anonymous

so youre saying when it is smaller than .4 it is rounded to 0

- nincompoop

but 1, 2, 3, 4, 5, 6, 7, 8, 9
tell me where is 8.1

- anonymous

so you're saying the answer is 8

- nincompoop

in scores 1 - 9 and if they are just 1, 2 .... 9
then yes
unless someone actually has a score of 8.1 then it is 8.1

- anonymous

so I tried 8.1 and 8 and it is saying it is wrong

- nincompoop

how about the first formula

- anonymous

the one that I used? nope

- nincompoop

I made a typo
\(\huge \frac{(B + 0.5E )}{n} \times 100 \)

- nincompoop

so 8.1 and 8.0 are wrong huh?

- anonymous

yes

- nincompoop

did you put 8.0 with point?

- anonymous

no I just did 8

- nincompoop

try 8.0 because of the 10th place value

- nincompoop

did it work?

- anonymous

wait but I only have one try left so I would like to be really sure!

- anonymous

the book says 8.2??

- nincompoop

I don't know what you just did in the end, kropot
but I do want to know why 8.2 because I want to learn if there's any other methods of solving this.

- anonymous

I am really not sure. They give me an example of "random number generator picks a number from 2 to 9 in a uniform manner. Find the 80th percentile(Round your answer to one decimal place . and the answer is 7.6
I am trying to work backwards from the answer but I still do not know

- dan815

(7.6-2)/(9-2)=0.8

- dan815

using same method,
(k-1)/(9-1)=0.9
k=?

- dan815

k=8.2

- anonymous

ohohoh I see

- anonymous

thank you so much for this explanation!!!!

- anonymous

what was the equation you used tho?

- dan815

i looked at the example they gave you

- dan815

basically what they are doing is

- dan815

|dw:1436852959460:dw|

- dan815

and they gave you this example |dw:1436853055768:dw|

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