To help you understand the algorithm, the video shows a simple two-digit by two-digit multiplication. You can see that the first and last digits are essentially the result of one multiplication.

Joke Torbeyns, Lieven Verschaffel, Mental computation or standard algorithm? Children's strategy choices on multi-digit subtractions, European Journal of Psychology of Education, Vol. 31, No. 2 (April ...

The Common Core State Standards teach students the algorithm for multi-digit addition and subtraction in 4th grade. But some experts say it should be taught sooner.