It is estimated that among customer type A the net profit is normally distributed with mean 450 and stdv 50.

If we do a box plot of net profit for a large sample of performance seekers, what's the proportion of performance seekers will be outliers according to the box plot?

upper inner fence = third quartile + 1.5(interquartile range)

lower inner fence = first quartile + 1.5(interquartile range)

The third quartile is 0.67 x stdv. But I don't know why?