Question 1196811
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The problem can be solved informally using logical reasoning, without algebra and without online calculators.<br>
Each type of burger uses one bun, so the total number of burgers is 12.<br>
All types of burger use at least one patty, and only the double cheeseburgers use two.  Since there are 12 buns and 15 beef patties, the number of double cheeseburgers must be 15-12 = 3.<br>
That means 12-3 = 9 of the burgers are either plain burgers or cheeseburgers.  The three double cheeseburgers use 6 of the 11 slices of cheese, so there are 11-6 =  5 slices for the single cheeseburgers; that of course means there need to be 5 plain cheeseburgers.<br>
3 double cheeseburgers and 5 plain cheeseburgers leaves 12-3-5 = 4 plain burgers.<br>
ANSWERS: 3 double cheeseburgers, 4 plain burgers, and 5 regular cheeseburgers.<br>