I bought two packets of apples, 25 in each packet. The mean and standard deviation of
weights of apples in the first packet are 235 and 3; and the mean and standard deviation for
the second packet are 237.5 and 4. Write down the mean and standard deviation formulae for
all the fifty apples and compute them.

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Answers

2015-04-05T01:27:11+05:30

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Combined mean =  ( μ₁ n₁ + μ₂ n₂) / (n₁ + n₂)
        = ( 25 * 235 + 25 * 237.5 ) / 50 = 236.25

combined standard deviation = [ (σ₁² n₁ + σ₂² * n₂) / (n₁+n₂) ]¹/²
       = [ (3² * 25 + 4² * 25) / 50 ]¹/²  = √12.5

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