Since you ALREADY purchased my "Composition Tutorial", which teaches what aspect ratio are :-), here is a free gift:
What do you do when your current graphic is 4X5 and you have to put it into a frame that is 9 inches wide? How long do you make the other side? We know we can cross multiply an divide (and come up with 11.5) but the kids may have trouble wrapping their heads around it.
This tutorial will show your students how to enter numbers into an Excel (or any other spreadsheet) sheet and do the formulas to cross-multiply and divide the number to "solve for X" and determine the missing measurement.