A sample of 35 observations has the mean 80 and S.D. as 4. A second sample of 65 observations from the same population has mean 70  and S.D 3. The S.D. of the combined sample is?

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Please find below the solution to the asked query:

Here ,n1=35, x1=80, σ1=4n2=65, x1=70, σ1=3x12¯=35×80+65×7035+65=73.5σ12¯=3516+42×25+659+12×25100=34.21=5.85

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