Good question ....
I've been interested on this for a few days so I thought of looking for a name.
What is the name of the branch of maths (if there is any) that deals with looking for shortcuts?
For instance, (99)(68) = 6732, 67 being (68-1), 32 being (99-68)
for the sake of mathematicality,
it is:
_{2}Φ_{99} = 10(χ-1)+(99-χ)
Let:
χ be the multiplicand
_{2}Φ_{11} = 10(χ+ β)+ α
Where:
χ is the multiplicand
α is the ones digit of the multiplicand
β is the tens digit of the multiplicand
and
_{2}Φ_{12}= 10[χ+(2α + γ)] + δ
Where:
χ is the multiplicand
α is the ones digit of the multiplicand
γ is 1 if β≥5, 0 if β≤4
δ is the last digit of 2α
there will be more after our semester break...