Calculating the resistance required to limit current in order to prevent diode burnout - I can't make sense of this textbook problem
I don't have that book to confirm, but look at the book's errata page on the publisher's website here (scroll about halfway down the page and click the "Errata" tab):

Wiley - Complete Electronics Self-Teaching Guide with Projects

You can see that a change was made to the question which did originally mention 1 ampere:


  Currently reads:
  
  The diode in the circuit shown in Figure 2-25 is known to break down at 100 volts, and it can safely pass 1 ampere without overheating. Find the resistance in this circuit that would limit the current to 1 ampere.
  
  Should be:
  
  The diode in the circuit shown in Figure 2-25 will break down at 100 volts, and it can safely pass 20 mA without overheating at that voltage. Find the resistance in this circuit that would limit the current to 20 mA.


So you can see that they changed the question. However it appears that in your edition (and perhaps in all editions, since the answer isn't mentioned in the errata) they forgot to change the answer!

Based on the new details in the question, your answer is indeed correct. Of course you should read the rest of the errata on that Wiley webpage, in case any of them also apply to your edition.

You might also want to read the comments on some parts of that book, in the "Spot The Mistakes" section, about one-third of the way down this page (search for the author's name Boysen):

http://www.talkingelectronics.com/projects/SpotMistakes/SpotMistakesP18.html

It seems to refer to an earlier edition of the book, since it shows the original "1 ampere" current in the question. However some of the other concerns mentioned there might also apply to your edition.