What is the difference between stupidity and ignorance?

Stupidity is when Ты are unintelligent, while with ignorance Ты may или may not be very smart but Ты just aren't very good at using your knowledge correctly.

Ignorance: when Ты simply don't know something, but Ты probably could learn it. A new person in train for example.

Stupidity: when Ты don't know something and probably can't learn it.

Ignorance is lack of knowledge.
Stupidity is lack of intelligence или common sense.
An intelligent person can be ignorant, and a stupid person can be knowledgeable.

stupidity means Ты have some knowledge but not a lot. Kinda like Dumb. But Ты can be Albert Einstein and not use your knowledge correctly или with any sense. that is being ignorant. :)