The best part of these "tricks" is that they'll also help you perform some simple calculations. Ready? Here we go!
A. Multiplying by 6.
If you multiply 6 by an even number, the answer will end with the same digit. The number in the tens place will be half of the number in the ones place. Example: 6 x 4 = 24
B. The answer is 2. (Wait, what's the question?)
Step 1. Think of a number. Step 2. Multiply it by 3. Step 3. Add 6. Step 4. Divide this number by 3. Then subtract the number from Step 1. (your original number) from the answer in Step 4. Example: 10 x3 +6 divided by 3 = 12. 12-10=2. The answer will always be 2!
C. The same three digit number
Step 1. Think of any 3-digit number where the numbers are all the same; 888, for instance. Step 2. Now add up the numbers (8+8+8= 24). Step 3. Divide the 3-digit number (like the 888) by the answer in Step 2. Your answer will always be 37.
D. Six digits become three.
Step 1. take any 3-digit number and write it twice to make a 6-digit number (ex 371371)
Step 2. Divide the number by 7. Step 3. Then divide it by 11. Step 4. Divide that number by 13. The answer will be your original 3-digit number. Be sure to do the division in order.
Example: 371371 divided by 7 divided by 11 divided by 13 = 371! A related trick is to take any 3-digit number (like 371) and multiply it by 7, 11, then 13. The result will be a repeating 6-digit number (371371). Pretty cool, eh?
E. Multiply large numbers in your head. (To easily multiply two double digit numbers, use their distance from 100 to simplify the math)
Step 1. Subtract each number from 100.
Step 2. Add these values together.
Step 3. 100 minus this number. This is the first part of your answer.
Step 4. Multiply the digits from Step 1. to get the second part of your answer.
F. Super-simple division rules. (You've got 210 pieces of pizza and want to know whether or not you can split them evenly within your group.) Rather than whip out the calculator, use these simple shortcuts to do the math in your head:
- Divisible by 2 if the last digit is a multiple of 2 (210).
- Divisible by 3 if the sum of the digits is divisible by 3 (522 because the digits add up to 9, which is divisible by 3).
- Divisible by 4 if the last two digits are divisible by 4 (2540 because 40 is divisible by 4).
- Divisible by 5 if the last digit is 0 or 5 (9905).
- Divisible by 6 if it passes the rules for both 2 and 3 (408).
- Divisible by 9 if the sum of the digits is divisible by 9 (6390 since 6 + 3 + 9 + 0 = 18, which is divisible by 9).
- Divisible by 10 if the number ends in a 0 (8910).
- Divisible by 12 if the rules for divisibility by 3 and 4 apply.
Wasn't that easy?
That concludes are math lesson for today. I hope you found it at least a little fun. It's still early here in Lily Pad so my brain isn't yet fully awake, but I can see where these tips and tricks will make doing math easier. Don't forget that tomorrow is Wednesday. And that means a visit from my wise mentor and friend, The Dharma Frog. I know you won't want to miss his lesson. So until then, I wish you
Helmenstine, Anne Marie, Ph.D. "10 Math Tricks That Will Blow Your Mind." ThoughtCo, Oct. 19, 2018, thoughtco.com/math-tricks-that-will-blow-your-mind-4154742.