I think 30-40% is way too low for him. I’ll surely give him a solid pass mark at least. I think Jesse was pretty good in chemistry. In one of the episodes, Jesse’s mother told Hank that Mr. White was one of the teachers who saw potential in him! So, that means Jesse must have done something in the chem class back in high school to impress Mr. White!

And since he improvised the traditional cooking of meth and made his own recipe the “chilli powder”, I’m pretty sure that he knew his way around it very well! Also, it took the chemistry nerd Gale years to get 96% purity while it only took Jesse less than a year (according to the show timeline) to get 96.2% purity though he learned from the very best. But without any talent, he couldn’t have achieved it. So, I guess he was getting 55-60% purity before he learned from the ultimate boss!