Thread: How many standard deviations of bell curve does it take to cover 85% of the data?

I know 1 std dev=68%, 2 sd=95%, 3=99.7%...can we compute a fraction of deviations that would get you 85% of the data?

If you have 85% inside the interval, then you'll have 15% outside the interval.

7.5% above
7.5% below

Find the z-score that corresponds to 0.075

(I'm using microsoft Excel to find this one, you can approximate it on a z-table)

z = -1.4395

so, basically, it will be 1.43 standard deviations above and below the mean that contains 85% of the data