Q4 of 33 Page 14

If the mean of the following data is 21.5, find the value of k:
          
xi 5 15 25 35 45
fi 6 4 3 k 2









xifixifi
5 6 30 
15 4 60 
25 3 75 
35 k 35k 
45290
Total15 + k255 + 35k

Mean =
= 21.5
21.5 (15 + k) = 255 + 35k
21.5 휕 + 21.5k = 255 + 35k
35k - 21.5k = 322.5 - 255
13.5k = 67.5
∴ k = = 5

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2 New Page 2 Find the mean marks from the following data:

Marks Number of Students
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Below 20
Below 30
Below 40
Below 50
Below 60
Below 70
Below 80
Below 90
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60
70
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0 10 20 30 40 50 60 70 100 90 75 50 25 15 5 0 

5 Find the values of f1 and f2 of the frequency, if the mean of the following frequency distribution is 21.4 and the total frequency is 40.
Class-interval 0 - 8 8 - 16 16 - 24 24 - 32 32 - 40
Frequency 6 f1 10 f2 9
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