Amazing maths tricks to astound, confound (and practice mental maths)
Want to be a mind reader? Have x-ray vision? No problem - you’ll just need a little bit of maths to get you going.
These maths tricks are great to play on your little ones, and with a bit of practice (which will come in handy for strengthening their maths muscle), they’ll be able to wow their friends too.
Mind reading dice
You probably know that the numbers opposite each other on a dice add up to 7 - you can use this knowledge in a trick to make your kids think you have x-ray vision, and also make them practice their 7 times table without them even realising it. First, get some dice...raid the Monopoly box if you have to!
Roll the dice and amaze your child by announcing the hidden face down numbers.
Well, given that you know that the opposite faces always add up to 7, then you know that if the top side is a 6, the bottom is a 1, and if the top is a 3, that the bottom is a 4 and so on.
Once you’ve convinced your kids that you’ve got super powers, you can let them in on the secret and they can try out the trick themselves. A bit of practice at this is a great way of reinforcing number bonds to 7 for younger children.
The next stage in this trick is to do it with a stack of dice.
Roll three dice and pile them on top of one another in a stack.
Tell your audience that you’re going to use your x-ray vision to see the hidden sides of the dice in the stack, and add them all up.
Because the opposite sides always add up to seven then this means that the top and bottom numbers on your stack of three will always add up to 21. (NB this works no matter how many dice you have, just multiply 7 by the number of dice.)
Let’s say the number at the top of the stack is 4. All you have to do is subtract this from 21
This means that the remaining top and bottom faces of the dice in the stack that are hidden will add up to 17.
Reveal the hidden dice sides one by one, adding as you go to reach the number you’ve predicted.
This trick uses the 7 times table and lots of single digit addition, which is great for working the maths muscle!
Ask your child to pick a number, any number.
Now double that number.
Then add 9.
Divide by 2.
And finally, subtract the original number.
The answer is always 3!
Mind-reading book trick
This trick is a slow burner and a real party piece. You’ll need a good thick book and some paper and a pencil for this one. Go to page 108 of the book and find the ninth word – write this word onto some paper and place it in an envelope.
Explain to your audience that you have written a word on a piece of paper which has been placed inside a sealed envelope. The following trick will reveal the word. Hand the pen and paper to an audience member and ask them to do the following:
Write down any three digit number.
Directly underneath it, write the number with the digits reversed, eg 321 becomes 123
Now take the smaller number away from the larger number eg 321-123 = 198
Now reverse the digits of this number (891)
Then add these last two numbers together, eg 198 + 891 = 1089
Hand them the book, and ask them to go to the page indicated by the first three numbers (108)
Once they’re on the page, tell them to go to the word indicated by the last number (9)
When they read out the word, ask them to open the envelope and show the exact word to the rest of the amazed audience.
After a bit of practice, get your child to try it at a family gathering and everyone will love it - give it a miss at the 9 year old’s birthday party though as it doesn’t have quite the same wow factor as pulling a rabbit out of a hat...
About Komodo – Komodo is a fun and effective way to boost primary maths skills. Designed for 5 to 11 year olds to use in the home, Komodo uses a little and often approach to learning maths (15 minutes, three to five times per week) that fits into the busy family routine. Komodo helps users develop fluency and confidence in maths – without keeping them at the screen for long.
And now we've got Komodo English too - check it out here.