I’ve recently started doing mental calculations and I’m using my own app to train mental multiplication. I’m currently using basic criss-cross method and it takes me about 60 secs to calculate a 5 digits by 5 digits multiplication.
I am thinking about how to improve criss-cross method to gain more speed.
Firstly, I think the intermediate additions are slowing me. How can I improve my addition speed? Secondly, is there any method to benefit from memorizing 2-digit related stuffs with criss-cross?