# Calculate faster than a calculator

Trick to multiply faster than a calculator.

If you have 2 numbers of two digits, where the first digits is the same in both numbers, then you can solve the multiply in this way:

$x = a \times 10 + b$
$y = a \times 10 + c$ where $b + c = 10$

Then:

$x \times y = [(a+1) \times a ] \bigcup [b \times c]$

For Example:

$64 \times 66 = (7 \times 6) \bigcup (6 \times 4) = 4224$
$51 \times 59 = (6 \times 5) \bigcup (1 \times 9) = 3009$
$83 \times 87 = (9 \times 8) \bigcup (3 \times 7) = 7221$

and so on:

$124 \times 126 = (13 \times 12) \bigcup (6 \times 4) = 15624$
$114 \times 116 = (12 \times 11) \bigcup (6 \times 4) = 13224$

If you have questions you can see this video: