Percentile question?

Question

Class (frequency)

10 - under 13 (7)

13 - under 16 (13)

16 - under 19 (5)

19 - under 22 (11)

22 - under 25 (1)

25 - under 28 (8)

28 - under 31 (3)

how to calculate the 75th percentile, 25th percentile and the median?

Answer 1

im just learning this now.

Interval   Frequency      

10-<13        7

13-<16        13

16-<19        5

19-<22        11

22-<25        1

25-<28        8

28-<31        3

you have to make a graph out of it in percentage, so you have to get class intervals and a cumulative frequency.

Interval   Frequency     CI            Cumulative F

                                      <10               0

10-<13        7                 <13               7

13-<16        13               <16               20

16-<19        5                 <19               25

19-<22        11               <22               36

22-<25        1                 <25               37

25-<28        8                 <28               45

28-<31        3                 <31               48

Now you have to make it into percentages and graph it.

CI            Cumulative F        %

<10               0                    0/48*100= 0

<13               7                    7/48*100= 15

<16               20                  42

<19               25                  52

<22               36                  75

<25               37                  77

<28               45                  94

<31               48                  100

Now you graph this putting percentage on the y axis and class interval on the x axis.

when you have done it on the y axis go to 25% and go across and wen you cross the line go down and thats wat the lower quartile is, etc

hope that helps, pretty confusing

Answer 2

You have 48 people there.  A quarter of that is 12.  The 25th percentile would be where you have 12 people - that would be in the middle of your 13-15 group.  The median would be at 24 people - that would be in your 16 - 18 group.  And so on.