Passive voice

I need some clarification regarding when it is appropriate to use the passive voice. In an essay I am writing, I use the passive voice twice in the first paragraph. I feel that by replacing the passive sentences with more active ones that I would obfuscate the intended meaning:

(Original paragraph with passive voice in bold)

My favorite class in college was Fundamental Immunology. Set-up differently than any course I had previously taken, one class a week was devoted to problem-solving questions. As randomly selected small groups, we were confronted with problems that covered material beyond our current level of knowledge. Collectively we used logic and previous study materials to answer these difficult problems. In addition to being a strong motivator to stay on top of the material, the race-against-the-clock setting made working together extremely important. We would throw out our ideas in rapid succession, and then weigh each other’s comments to decide upon a final answer.



The passive voice in these sentences is used because the professors and TAs who administered the class are not important. But from a purely stylistic point of view, I am uncomfortable using the passive voice. Any suggestions?