As a San Diego math tutor myself, I use this trick to divide numbers quickly, and without the use of a calculator. This short lesson will allow you to make fast educated guesses. In this article, we will go over the easy number tricks. I can honestly say that I use these every single day.
Number 1 – All numbers are divisible by 1.
Number 2 – All even numbers are divisible by 2.
Number 3 - If you add up all the digits in a number, and the result is divisible by 3, then the number is as well. Example 342. 3+4+2=9 And since 9 is divisible by 3, so is 342. 342/3=114
Number 4 – If the last two digits of a number is divisible by 4, then so is the number. Example: 232 since 32 is divisible by 4 so is 232. And 232/4=58
Number 5 – If the number ends in a 0 or a 5, then the number is divisible by 5.
Number 6 - If a number is divisible by 2 and 3, then it is divisible by 6. You just need to combine rules 2 and 3. Example 42. Since it is even it is divisible by 2. Since 4+2= 6 and 6 is divisible by 3, then 42 is divisible by 6. And 42/6=7.
Number 9 – If the sum of the digits is divisible by 9, then the number is divisible by 9. Example 5,256. Since 5+2+5+6=18, and 18 is divisible by 9. 5,256 is divisible by 9. 5,256/9=584.
Numbers 7, and 8 are a bit more complicated, and we will save them for another time. I hope this trick of a San Diego math tutor, will help you do more mental math not only is school, but in your everyday life. Look for more tips and tricks every week from your San Diego math tutor at AheadoftheCurveTutoring.com