Not necessary, because although we know that preventive medicine decreases medical costs greatly, the argument doesn’t rely on any specific aspect of preventive medicine that reduces those costs. We don’t know, for example, whether the lower cost must be due to using technologies that are lower in cost.

Not necessary, because the author doesn’t have to commit to some specific numerical relationship between hours teaching and cost savings. We know the author thinks that more time spent on preventive medicine would reduce costs, but that doesn’t imply a 1 hour to 10% cost reduction ratio. Maybe an extra hour of instruction would only decrease costs by 1% or 0.5%; that doesn’t undermine the author’s argument.

Not necessary, because the author may believe that medical schools would only need to adjust the balance of preventive vs. curative teaching. The author isn’t committed to the idea that medical schools need to increase the overall amount of teaching hours in order to become more cost-effective.

Not necessary, because even if improvements in curative medicine techniques do NOT increase medical costs, we still know from a premise that preventive medicine decreases costs greatly. As long as preventive medicine is currently more cost effective than curative medicine, it doesn’t undermine the argument to learn that curative medicine won’t increase in the future.

Necessary, because if it were not true — if the time required to teach preventive medicine thoroughly is NOT more than 1 hour for every 10 spent on curative (in other words, if the current time spent on preventive medicine is enough to teach it thoroughly) — then we have no reason to think that schools aren’t spending enough time on preventive medicine. Additional time wouldn’t be expected to increase cost-effectiveness, because it wouldn’t be expected to improve students’ use of preventive medicine.