cnu115 2 years ago On an exam, a class ended with a mean raw score of 80 with standard deviation of 10. The distribution of grades in the class was approximately normal. If the teacher wants to give "A" to the top 25th percentile (top 25%) of the class, what is the lowest raw score we could get and still get an "A" on the exam?

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1. dan815

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2. cnu115

standard deviation of 10

3. dan815

lol i mean how many deviation points wud u have to travel, to be left with only 25% area on the right side

4. dan815

look up the probability distribution graph numbers

5. cnu115

6. dan815
7. dan815

look at that and see at what standard deviation you have to be to be left with only 25% area on the right side

8. dan815

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9. cnu115

Is it 21% with 0.8 standard deviation?

10. cnu115

It is only one standard deviation point above the mean is to be covered. Isn't it? Other please explain

11. dan815

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12. dan815

how much more deviation does she have to go to cover upto 75%

13. dan815

look at that chart and figure it out

14. dan815

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15. dan815

its somewhre inbetween 0.5 and 1

16. dan815

id say around 0.75

17. dan815

so 0.75 of 10 = ? 7.5 marks

18. dan815

then 87.5 should be the marks she needs to set it at

19. dan815

im just estimating values here, im sure u got some formulas to calculate the exact z values and stuff

20. dan815

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21. cnu115

22. dan815

this will give u more accurate vlaue

23. dan815

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24. dan815

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25. dan815

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26. dan815

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27. dan815

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28. dan815

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29. cnu115

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30. cnu115

what is this equation you have used

31. dan815

5.6/15

32. dan815

because

33. dan815

look at the chart

34. dan815

at 0.5 deviation on right how much percent have you covered?

35. cnu115

and how did you get 0.37

36. dan815

37. cnu115

????? 5*6/15=0.37 ????

38. dan815

whats the answer supposed to be

39. dan815

its 5.6 not 5 * 6

40. dan815

41. cnu115

42. dan815

then dont bother with stuff

43. dan815

first understand the graph

44. cnu115

45. cnu115

Ok sir

46. dan815
47. dan815

the graph is pretty self explanatory and questions about it?

48. dan815

any questions?

49. cnu115

just a second sir,

50. cnu115

Now it is clear. But one question. May I ask

51. cnu115

Why did you divide by 15. It is only 14 parts. Right

52. cnu115

Sorry. Now I have fully understood.

53. cnu115

It is not the 14 parts. It is the area of that part.

54. cnu115

Thank you very much explaining in detailed manner

55. cnu115

Thanks for your patience and analysing for a lehman.

Mean 80 standard deviation 10 z=-0.67 X=73.3

mine answer is 73.3 marks min to get A

you have to take Z value -0.67

59. dan815

musadiq no try taking 0.67 Z