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Means and standard deviations of the sco...

Means and standard deviations of the scores of an intelligence test of two classes of different sizes of 25 and 75 are `M_(1) = 80` makrs and `M_(2) = 85` marks and S.D. = 15 marks and S.D = 20 marks
Calculate the combined mean and the standard deviation of the two classes.

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The correct Answer is:
Mean = 83.75 marks, S.D = 19 marks
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