Photo postage

Stamps.com is restarting their photo postage program (does it count for alliteration if the p sounds like f?) on May 17. And they're going for people's philatelic side with the offer of special "first day" banners for people who order by the 16th. I can so see this becoming a trendy thing for weddings and baby announcements...

1. A sheet of 20 $.37 stamps costs $16.99.
   1. How much extra (above the face value of the stamp) are you paying per sheet? Per stamp?
      
   2. If you buy 10 sheets, the cost is $13.99 each. How much extra are you paying per sheet? Per stamp?
      
   3. Is it worth buying 10 sheets? Explain your reasoning.
   
   
2. According to a news story,
   "The initial 7.5 -week test sparked orders for more than 2.7 million stamps and generated $2.3 million in revenue. Of the 83,000 images submitted, nine inappropriate images were made into stamps."
   1. What was the average number of stamps ordered per week?
      
   2. How much revenue did the company earn per stamp?
      
   3. What percent of images were appropriate?