Not at all. I just did that one in my head while driving, though I'm not fast. The original multiplicands are honestly the hardest to remember. Don't materiali

Not at all. I just did that one in my head while driving, though I'm not fast. The original multiplicands are honestly the hardest to remember. Don't materialize all of the intermediate results, and you can stay within working memory. You'll need to chunk a little, but mostly only 2 digit numbers. Personally, I use fingers to keep track of the 10s place, and work from left to right. Less overwriting that way, and you start with an underapproximation that you refine gradually, which means you can stop early when estimating.