Question

Suppose that the readings on the thermometers are normally distributed with a mean of 0∘ and a standard deviation of 1.00∘C.
If 8% of the thermometers are rejected because they have readings that are too high, but all other thermometers are acceptable, find the reading that separates the rejected thermometers from the others.

Answer 1

Draw a sketch of what you want, similar to this:
http://prntscr.com/8kitsp

THen look up the standard normal distribution table (left tail) the number of standard deviations that correspond to 92%. (it should be between 1.4 and 1.5).
Since each standard deviation corresponds to 1°, so you can figure out the cut-off temperature.

Answer 2

or, you can play around with Z values and areas at

http://davidmlane.com/hyperstat/z_table.html