New Multiplication B

How to multiply 2 triple-digit numbers
whose hundreds digits are both one (1).

104 x 117 = (100 + 4)(100 + 17)
= 10000 + 1700 + 400 + 68
= 12168

112 x 105 = (100 + 12)(100 + 5)
= 10000 + 500 + 1200 + 60
= 11760

The pattern is:
Note: r & s represent double-digit numbers.

1r x 1s = (100 + r)(100 + s)
= 10000 + 100s + 100r + rs
= 100 + 100(r+s) + rs
= 100 + 100(sum of numbers) + product of numbers

And the above two examples can now
be calculated mentally as follows -

104 x 117 = 10000 + 100(4+17)+ 68
= 10000 + 2100 + 68
= 12168

112 x 105 = 10000 + 100(12+5)+ 60
= 10000 + 1700 + 60
= 11760

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