How can we help?

(Writing this as an 8th-grade student) I honestly taught myself how to do this. It's definitely way easier than multiplying 9s normally, and its consistent too. You just add 10 to (x) multiple of 9 then subtract 1, and boom, you have the answer.

EX:
9 + 10 - 1 = 18 (9*2)
18 + 10 - 1 = 27 (9*3)
27 + 10 - 1 = 36 (9*4)

and you could just go on forever with it. Teachers should definitely teach this method more often in my opinion.

JDOG, using your method, for 9 x 8, you would have to calculate all the multiples that preceded 8.  That involves almost 30 numbers and 8 calculations.  No way this replaces memorization.

Are you familiar with Make10?  It's usually taught in K/1st grade.  It's the intro to mental math where students learn to break apart numbers and put them back together.  For 8 + 5, you Make10 out of the 8 with 2, which leaves 3 left over.  10 + 3 = 13.

The calculation above simply requires that you Make10 out of the multiplier...but just before you do, name the digit that comes before it.  So..the digit that comes before 8 is 7 (for 70) and you Make10 out of the 8 with a 2.  Answer:  72.

K/1st graders are required to know how to count back from 10.  They memorize the order, so the first step is not even a calculation.  Just name the digit that proceeds 8.  Spit second used.

They are also required to be proficient at Make10.  It is a "must-have skill."  It is an instantaneous calc b/c the mind fills the space between the digit in question (8) and 10.  The mind snaps forward to the 10 because it is 'magnetic'.

Bottom line, try it with an early elementary school student who knows Make10.  It takes about a minute for them to learn how to pair this two-step and you will save them ~2 hours otherwise wasted memorizing the 9-multiples.  If the student shares it with classmates, 60 hours are saved.  One day, educational websites will share and 8 million hours will be saved (year after year).  Greg