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salman_09
a class has 3 sections SECTION ONE has (22 students), (avg score = 68), (SD = 9) SECTION TWO has (25 students), (avg score = 75), (SD = 9) SECTION three has (32 students), (avg score = 60), (SD = 9) WHAT IS THE Standard deviation OF CLASS ?
avg = (22*68 + 25*75 + 32*60) / (22 + 25 + 32) not sure about the std