Improving criss-cross

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?

Some tips that helped me:

  • start each new answer-digit with the carry digit, before adding on the times tables.
  • have a set order that you do the calculations in. For ABCDE × VWXYZ, 5th digit, I’d start with A×Z and V×E before proceeding “inwards”.
  • make sure you’re super fast with the 2×2 to 9×9 times tables, so there is no friction.
  • make sure your phonological loop is not slowing you down; all your processing should be visual.

I have specific drills for my own practice for the last two points.

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Thanks for the tips. I understood your first tip as writing down the carry digits first and summing in the end. Is this right? Also the idea suppressing phonological loop seems to be interesting. Is something like visualizing digits the way to go?

You can also train your two digits addition using flash anzan, It should improve your criss Cross multiplication.

For criss-cross multiplication you don’t need to write down anything except for the answer :slight_smile: But for each new digit of the answer, start with the carry digit, and add on the criss-cross contributions afterwards.

I’ve written an in-depth guide here: How to Multiply Large Numbers in Your Head (Cross Multiplication) – World Mental Calculation

Visualizing in some way is the way to go for sure, if you want speed. All the fast people are using their inner voice almost zero for multiplications. Some prefer to use the soroban/abacus, but otherwise (like Freddis Reyes, who had the world record for many years, and Marc Jornet Sanz, the current record-holder) you can do just as well just imagining the number in your head, which simply takes practice.