shrewreadings:northray:saranna2195:…Ok why didn’t someone teach me this magic?The 9-rule - for when
shrewreadings:northray:saranna2195:…Ok why didn’t someone teach me this magic?The 9-rule - for when you’re not writing them all down. The digits of a multiple of 9 will always add up to 9 (or some multiple of 9, once you get past 10.)1 - 10: To find the first digit, subtract 1 from the number that isn’t 9: the 2nd digit is what you’d add to get to 9. 7x9: subtract 1 from 7, you get 6. Something + 6 = 9. It’s 3, so7x9 = 6312: (10 + 2) x 9 = (9*10) + (9*2) = 90 + 18 = 108; 1+8 =9…Handy tricks for sneaking ideas like algebra and distributive laws into kids’ heads so they don’t get freaked out in middle school. -- source link