Someone here referenced a psychologist teaching their son or daughter the finger trick with regard to multiplying by 9 - and then someone else said, oh yes, I know that one, but the such and such trick is great, too. I don't know any of them! Could you please share?

Also, when I was in grade school (you can tell how old I am from that statement!), my French teacher taught me a trick re: checking your work on large number multiplication. It was something like adding up all the numbers separately in the products and the result, and keep adding them, and the 9's are counted as 0's and each part should equal the result. Clearly, I can't remember it - but maybe it's enough to get someone here to tell me what it is. I know it helped me throughout school when I was required to multiply large numbers. It's probably outdated, but it was a neat trick.

Thanks.