lmw,

Good job. You're on the right track, and we like to see students try out problems before posting.

Draw a picture of the normal curve, centered at 0.15mm, with tick marks going out for each std dev +1, +2, +3 and -1, -2, -3. You should see that the rejection region for the parts is <= 0.14 and >=0.16, which correspond to z scores of -2.00 and +2.00.

Now, just find the proportion of the area under the normal curve outside of -2 and +2. Hint - it's pretty small.

JohnM