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Daily profit interval

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A trader's daily profit has sample standard deviation $s = 20$ over $n = 100$ days. The confidence interval for the mean profit has half-width $h = 2 \times \frac{s}{n}$ . What is $h$ ?

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Hint

Compute the square root of the number of days first.

Solution

The half-width is $h = 2 \times \frac{s}{n}$ .
Here $n = 100 = 10$ .
So the standard error is $\frac{s}{n} = \frac{20}{10} = 2$ .
Multiplying by the factor gives $2 \times 2 = 4$ .
So the half-width is $4$ .

Answer: $4$

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