the number of dvd rented by each of four families in the past month is 8,4,16 and 2. use the samole size of 3. find the mean and standard deviation
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The mean is (8+4+16+2)/4=30/4=7.5.

The variance is ((8-7.5)^2+(4-7.5)^2+(16-7.5)^2+(2-7.5)^2)/4=115/4=28.75.

Standard deviation is √28.75=5.36.

This would give us 7.5±5.36 for the number of DVDs.

I'm not sure why 3 has been given as the sample size, but I assume that the standard deviation is to be calculated using 3 instead of 4 as the divisor. This means SD=√(115/3)=6.19 and the number of DVDs rented is 7.5±6.19 or the range 1.31 to 13.69.

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