5th practice set. do i use the same SD of 1 degree for each set or should it change as I go down the problem. its all part of one question and i have spent over an hour getting the wrong answer. please explain so i can see where i keep making my error.

For 17, 21, 29, 49, 51, the standard normal distribution is given. More specifically, we have a data set of thermometer readings that are normally distributed with a mean of 0 degrees Celsius and a standard deviation of 1 degree Celsius. A thermometer is randomly selected and tested. Find the probability that a reading is.... #17 less than -1.5 #21 greater than 2.22. #29 between -1.2 and 1.95 #49 Find Pos. This is the temperature reading separating the bottom 1% from the top 95%. #51 If 2.5% of the thermometers are rejected because they have readings that are too high, and another 2.5% are rejected because they have readings that are too low, find the 2 readings that are cutoff values separating the rejected thermometers from the others