Bigger is not always better

I found the post on http://www.athriftymom.com/ about buying a bulk item with a high value coupon. So basically here is the example she used.

say you have a $2 off coupon for chinet plates 36-72 count.
the 36 count plates are $2.50 and the 72 count plates are $4.50. Buying at the regular price the 72 count plates is a better deal. When you use the coupon the 36 count plates are $.50 a pack making them a little over $.01 per plate. If you bought the 72 count plate it would be $2.5 for the pack making them a little over $.03 per plate.