quick trick: mind-blowing math tricks

We are. Dealing with a math hater in our house so I’m looking back at your old posts for some inspiration. Here’s two tricks I learned: one is for 6×6 through 10×10. There is a video going around for that. It’s like the nines trick. I think you can google it and find it. The other was a Vedic math trick (say what?) for multiplying two digit numbers. It involves drawing intersecting lines and counting the cross points. It’s another video. I can’t explain well but if you’re interested I’ll send you the links.

Another math trick I found helpful when helping students learn multiplication of numbers 6-10x 6-10, is if you hold both hands up, treat thumbs as number 6, pointer as 7, middle as 8, ring as 9, and pinky as 10. Then pick what numbers you want to multiply, for example, 8×9, you would place your left hand middle finger with your right hand ring. All the fingers “below” and including those fingers (left hand: middle, pointer, thumb, right hand: thumb, pointer, middle, ring) would be considered tens. You just count these fingers and add together, therefore you have 7 tens or 70. Then the finger above you multiply each hand as if the number of fingers are ones. So the left hand has 2 (ring and pinky) and the right hand has one (pinky), so 2×1=2. Then you add the tens places and ones places to get 72, which is 8×9. Some fingers are harder or easier depending on if you have to carry from ones place. Hope this was another idea!

I’m a retired elementary school teacher, and I’ve picked up a few Math tricks over the years. I’ve even come up with a few myself.

The 9 multiplication table has lots of tricks. The first is one that most people know, which I call “Count Up – Count Down”:
First, on a piece of paper, write a column of numbers starting at 0 and stopping at 9. Next, beside that column, write another one starting at 9 and count down to 0. You will then have the 9 times table.
0 9
1 8
2 7
3 6
4 5
5 4
6 3
7 2
8 1
9 0.
Let’s go further with this. “Cut” the table in half between 45 and 54. “Slide” the bottom half of the table up to the right of the top half. You will get:
0 9 9 0
1 8 8 1
2 7 7 2
3 6 6 3
4 5 5 4
It’s like they’re mirror images of each other… 1 8 and 8 1, 3 6 and 6 3, etc.
Also add the digits of each multiple, and you get 9… 0 + 9 = 9, 4 + 5 = 9, etc.
And when you multiply 9 by any whole number, no matter how big or small, the digits in that number will add up to 9, as well (which can also be used to see if a large number can be divided by 9 with no remainder).

The 8 multiplication table follows an interesting pattern all its own. Look at the 8 table. The numbers in the ones place follow the pattern 8 – 6 – 4 – 2 – 0 (basically counting backwards by 2).
Now it’s time to figure out what goes in front of those numbers, another pattern. Count by ones, starting in front of the first 6, but use each fourth number twice: 1 – 2 – 3 – 4 – 4 – 5 – 6 – 7 – 8 – 8 – 9 – 10 – 11 – 12 – 12, etc.
Put it together and you get…
8 8 8
1 6 9 6
2 4 10 4
3 2 11 2
4 0 12 0
4 8 12 8
5 6 13 6
6 4 14 4
7 2 15 2
8 0 16 0
The pattern goes on forever…

Now, everyone from 1st grade on up can count by 5. You can use that to get the 6 times table, using either tally marks or your fingers.
For tally marks: As you count by 5, make the tally mark symbol each time you count out a multiple of 5, but add an extra mark for each one because you’re really counting by 6. Let’s take the example of 6 x 7. When you finish making the tally Mark’s, you should have 7 of the 5 symbols, each with the extra mark beside it to represent 6. Now recount the 5’s… 5, 10, 15, 20, 25, 30, 35… now count the single tally marks starting with the next highest number above the last number you counted, 36 in this case… 36, 37, 38, 39, 40, 41, 42. In our example, you’ve run out of tally marks and you’ve got your answer, 6 x 7 = 42.
This can also be done on your fingers: Count by five, raising a finger from your fists with each count. Using our previous example, when you reach 35, you should have 7 fingers sticking up. Put the fingers down one at a time, counting by ones as you do. Once all your fingers are down, the last number will be 42.

And just for fun, there are a couple of odd multiplication problems with their own pattern:
1 2 = 3 x 4 and 5 6 = 7 x 8
Do you see it? Take out the Math symbols.
1 2 = 3 x 4 5 6 = 7 x 8
1 2 3 4 5 6 7 8
1 2 3 4 5 6 7 8
Those are the only two problems I know of that does that.

I have so many Math tricks, that my old colleagues and friends often suggested that I write a book, not just for teachers, but also for parents and their children. Now that I’m retired, I’ve actually started on the project.