Shrinking the standard error

EasyStatistics~3m

A single measurement has standard deviation $20$ . You currently average $4$ independent measurements. How many additional measurements must you take so that the standard error of the average is halved?

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Current SE $=20/\sqrt4=10$ ; you want it to reach $5$ .
Solve $20/\sqrt n=5$ for $n$ , then subtract the $4$ you already have.

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Shrinking the standard error

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