math
posted by Lauren .
A word
Problem
Kris has an endless supply of 4cent and 7cent stamps for mailing a package. What is the greatest amount of postage that cannot be affixed to a package using these stamps?

basically what is the gcm that these canot be..
easiest way...make a list
4,7,8,11,12,14,15,16,18,19,20,21,22,..... so the highest # is 17