Answer:
Represent the mark on frequency table as follows;
Marks Frequency
40 3
50 4
60 3
70 6
80 3
90 1
Mean= Sum of all the marks
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Frequency
(40×3)+(50×4)+(60×3)+(70×6)+(80×3)+(90×1)
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20
=2250
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20
=11.5