Hey spacemenon.

What I think they mean by this question is that you need to have a value that is less than 0.001. If you choose for example 0.0009 then the answer you get for n is 81.84179 which gives an answer for n = 82 (which is in agreement with the textbook answer).

Remember that it has to be less than 0.001 which means you can't actually use 0.001 but a value that is lower and for this I choose one decimal unit down from 0.001 which is 0.0009.

I use the same technique you used just with a different critical value.