Isn't actually just impossible for it to do it well on arbitrarily large inputs like this even from computational complexity point of view. If it doens't know it's allowed to do step by step multiplication (addition is maybe ok). I'm not sure it's a criticism against its ability to reason. It's similar to asking someone to do addition in 5 seconds with no paper. like of course at some point it won't be able to do it for a large enough number. BTW strongly disagree that the average grade schooler will be able to add 2 30digit numbers even with paper without making a mistake.