Question

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

Answer 1

why did you use that "set up?"

Answer 2

in my book it says to use it

Answer 3

(base)(height)=0.90

Answer 4

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

Answer 5

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

Answer 6

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

Answer 7

right

Answer 8

how would you look for that number

Answer 9

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

Answer 10

let us list your numbers

Answer 11

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

Answer 12

okay yes

Answer 13

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:
\(\sf \huge \frac{B}{n} \times 100 \)

Answer 14

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

Answer 15

so it would be 8.1?

Answer 16

8?

Answer 17

I thought it ment to keep the .1

Answer 18

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

Answer 19

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

Answer 20

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

Answer 21

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

Answer 22

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

Answer 23

8 out 9 makes almost 90%

Answer 24

no

Answer 25

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

Answer 26

the .6 is kept

Answer 27

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

Answer 28

you're right
you keep it

Answer 29

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

Answer 30

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

Answer 31

so you're saying the answer is 8

Answer 32

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

Answer 33

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

Answer 34

how about the first formula

Answer 35

the one that I used? nope

Answer 36

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

Answer 37

so 8.1 and 8.0 are wrong huh?

Answer 38

yes

Answer 39

did you put 8.0 with point?

Answer 40

no I just did 8

Answer 41

try 8.0 because of the 10th place value

Answer 42

did it work?

Answer 43

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

Answer 44

the book says 8.2??

Answer 45

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.

Answer 46

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

Answer 47

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

Answer 48

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

Answer 49

k=8.2

Answer 50

ohohoh I see

Answer 51

thank you so much for this explanation!!!!

Answer 52

what was the equation you used tho?

Answer 53

i looked at the example they gave you

Answer 54

basically what they are doing is