MMG 302 - Dilutions Worksheet

In MMG 302 students are required to use basic mathematics to go through both dilutions of bacteria and solutions throughout the semester.  Much to my chagrin, this proves to be a difficult task.  Most students merely memorize the formulas provided and never take the time to understand the steps (I assume this is a common problem in math courses everywhere).  

I had first created and used this worksheet while teaching BS 171 and I altered and applied it to the materials within this class.  I sent it out to the students class-wide and those who took the time to go through it said it helped them a lot.  After going through my teaching class (ISE 870) I learned why this worksheet is so effective.  I did not rely on a single formulaic example, and by 'mixing it up' the students are forced to understand the concepts instead of merely the way to solve a single problem.  

In addition I sent out an "answer key" containing not only the answers to the problems but the method(s) by which I solved them.  I assumed that this would help the students more than simply providing the answers.  Thus, if their answer was wrong they could go through the steps I provided and see where there mistake lies.

I have included the worksheet below.

Closing question:  Does anyone have any suggestions on alternative questions that would help them open their minds and truly understand what's going on?