I enjoy writing someone trying to be scientific, and doing better than average when compared to many characters in fiction, but still an amateur who, to a degree, is muddling through things with statistically insignificant data sets.
Completely unrelated, but I like Mythbusters.
Grace, meanwhile, would just instantly know the answer (24,601).
I, too, cannot do multiplication like that quickly in my head. I can do it, I know my basic multiplication tables and such, but I'm nowhere near fast enough to justify not using a calculator, and I could easily make a mistake at each step.
Also, once any of the numbers get a third digit involved, I declare "NOPE."
I know how to do it, but with how easily I get sidetracked, my short term memory is like an excitable dog that's going to lose track of everything at any moment. I'm writing it down, or I'm using a calculator. That simple.
Which, fortunately for me, is simple enough these days. Apologies to my former math teachers, but it is now more common than not to have quick access to a calculator at almost all times (we were once warned this would not be the case).
Granted, maybe I'd be better at doing multiplication in my head were that not the case, but I'm not going to complain about not having to.