## anonymous one year ago 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

1. nincompoop

why did you use that "set up?"

2. anonymous

in my book it says to use it

3. anonymous

(base)(height)=0.90

4. nincompoop

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

5. anonymous

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

6. nincompoop

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

7. anonymous

right

8. nincompoop

how would you look for that number

9. anonymous

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

10. nincompoop

11. nincompoop

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

12. anonymous

okay yes

13. 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: $$\sf \huge \frac{B}{n} \times 100$$

14. 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

15. anonymous

so it would be 8.1?

16. anonymous

8?

17. anonymous

I thought it ment to keep the .1

18. nincompoop
19. nincompoop

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

20. 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

21. nincompoop

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

22. 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

23. nincompoop

8 out 9 makes almost 90%

24. nincompoop

no

25. anonymous

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

26. anonymous

the .6 is kept

27. nincompoop
28. nincompoop

you're right you keep it

29. anonymous

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

30. nincompoop

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

31. anonymous

so you're saying the answer is 8

32. 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

33. anonymous

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

34. nincompoop

35. anonymous

the one that I used? nope

36. nincompoop

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

37. nincompoop

so 8.1 and 8.0 are wrong huh?

38. anonymous

yes

39. nincompoop

did you put 8.0 with point?

40. anonymous

no I just did 8

41. nincompoop

try 8.0 because of the 10th place value

42. nincompoop

did it work?

43. anonymous

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

44. anonymous

the book says 8.2??

45. 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.

46. 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

47. dan815

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

48. dan815

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

49. dan815

k=8.2

50. anonymous

ohohoh I see

51. anonymous

thank you so much for this explanation!!!!

52. anonymous

what was the equation you used tho?

53. dan815

i looked at the example they gave you

54. dan815

basically what they are doing is

55. dan815

|dw:1436852959460:dw|

56. dan815

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