Harold took 5 hours to paint 3 same-sized walls. If he works at the same rate, how long will it take him to paint 18 walls of th
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We want the integral of the standard normal from -z to z to be 0.85. Let's look at some standard normal tables and pick the right one.
It's easy to find the Erf one, which is the integral of the unit normal from 0 to z. That will be exactly half of the integral from -z to z. So we look for the z value corresponding to a probability of 0.425 in that table and find
z = 1.44
Answer: 1.44
[figure from Wikipedia]
