statistics

The following frequency distribution presents a set of exam scores for a class of N= 20 students.

X F CF % C%
90-99 4 20 20 100
80-89 7 16 35 80
70-79 4 9 20 45
60-69 3 5 15 25
50-89 2 2 10 10
a)Using interpolation find the 30th percentile.

The answer I came up with was 72.

B) FIND THE 88TH PERCENTILE

93.5

C) WHAT IS THE PERCENTILE RANK FOR X=77

40th percentile

D) WHAT IS THE PERCENTILE RANK FOR X=90

81st percentile

-Are my answers correct. I did the % portion of the table myself. I'm not sure if I did it correctly though.

Thank You

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  1. I realize the table looks off. X= the scores 93-95...etc. cf= 4,7,4,3,2,. %=20,35,20,15,10. c%=100,80,45,25,10.

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