Follow
(A+B)*(E+F)=A*E+A*F+B*E+B*F
for example
39*27 = (30+9)*(20+7)
39*27=30*20+30*7+9*20+9*7
39*27 = 600+210+180+63
39*27=810+243 = 1053
It is very possible to do these kind of problems in your head while walking with enough practice but it might take a long time
@shortstories
Associative and commutative laws of addition/multiplication.
I used to do the same kind of mental math when I was bored. You sound similar to me, but with your tism dial set higher than mine.