Speaking of "cool" math tricks... this one even impressed his mom, who doesn't generally give a hoot about this kind of stuff.
And if any of you already know this, please bear with me... it's new to us & we've been giddy as all get out.
Multiplying numbers by 11 made easy:
2-digit:
Concatenate 1st digit, sum of 1st & 2nd, 2nd digit
23 x 11
2|2+3|3
2|5|3
253
3-digit
Concatenate:
1st digit|sum of 1st & 2nd|sum of 2nd & 3rd|3rd digit
245 x 11
2|2+4|4+5|5
2|6|9|5
2695
And so on...
When you have some sums greater than 10 in the middle, you have to carry back the one, but it's still very easy.
Class dismissed, now go amaze (or frighten) your friends & family!
