Encrypt the 2 digits multiplication table in my mind

[Josh (Josh Cohen)]

I removed the personal information from the post. It’s better to use private messages for that.

[only4u]

@Antelex

5. x55 means half and half
   38x55 → [38/2=19] → 1900+190 → 2090
   87x55 → [87/2=43.5] → 4350+435 → 4785

6. Double digits type a:
   33x26 → 3x2|[2+6=8]x3|3x6 → 6_24_18 → 858;
   42x88 → 4x8|[4+2=6]x8|2x8 → 32_48_16 → 3696;

7. Double digits type c:
   The tens digit is equal and the units digit add up to 10.
   66x64 → 6x[6+1=7]|6x4 → 4224
   23x27 → 2x[2+1=3]|3x7 → 621

in 5.[x55] and 8.[x double digit type a] you can use your 1. [x11]
example =
42x88= 42x[8x11]=336x11=3[3+3][3+6]6=3696

also in 10.[double digit type c]
if the tens digit is same and unit digit adds upto 10 then
multiply the same digit with next digit and multiply unit digit
66x64 heresame tens digit 6+4=10
so answer= [6x7][6x4]=4224

also i want to know are you using this calculation only mentally or do you also use it on paper?

is criss cross method faster then doing multiplication by breaking one number and then multiplying it ?e.g. 78x42 = 78x40+78x2

i am trying to increase my calculation speed so your insight and any suggestions are welcome