Same tens digit? Instantly multiply them

This trick is a great one.
It uses an amalgamation of other mental math techniques - and will have you smashing those calculations.

Here is THE mental multiplication lesson playlist - progressing you through your mental multiplication.
https://www.youtube.com/playli....st?list=PLjbxBzUM6SL

Here is that link how to multiply questions like 49 x 40 instantly
https://youtu.be/yZULgerBRms

The rest are links where I beg for money.

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