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# Standard Deviation Question! Watch

1. 1) The mean and standard deviation of the heights of 12 boys in a class are 148.8 cm and 5.4 cm respectively. A boy of height 153.4 cm joins the class. Find the standard deviation of the heights of the 13 boys.

Firstly, I calculated the new mean which is 149.15 cm, but I don't know what to do know, how do I calculate the new S.D with just this data given?
2. You know the 'old' standard deviation. You know the 'new' value (for the 13th boy) and the 'new' mean so you know how close the new boy is to the new mean. So can you not use this to amend the standard deviation?

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Updated: December 7, 2010
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