At present, the formula for primary school students to learn "primary ninety-nine" is from "11" to "998 1", while in ancient times it was the other way around, from "998 1" to "224".

Because the first two words of the formula are "99", people call it "Xiao 99" for short. It was only in the 13 and 14 centuries that it turned into the present situation.

Multiplication and carry system has existed in ancient Babylon for a long time, but the operation process is not as simple and fast as formula 99, and it is not easy to remember.

The multiplication formula of modern pupils is as follows:

1× 1= 1

1×2=22×2=4

1×3=32×3=63×3=9

1×4=42×4=83×4= 124×4= 16

1×5=52×5= 103×5= 154×5=205×5=25

1×6=62×6= 123×6= 184×6=245×6=306×6=36

1×7=72×7= 143×7=2 14×7=285×7=356×7=427×7=49

1×8=82×8= 163×8=244×8=325×8=406×8=487×8=568×8=64

1×9=92×9= 183×9=274×9=365×9=456×9=547×9=638×9=729×9=8 1

China used the "99 formula" earlier. Sentences such as "3927", "684 18", "483 12" and "6636" can be found in books such as Xunzi, Guanzi, Huainanzi and Warring States Policy. It can be seen that as early as the Spring and Autumn Period and the Warring States Period, 99 multiplication songs became popular.