Category Archives: math tricks

Squaring Off

Can you create a square that is exactly 5 square inches in area? This activity will show you how.

Gather a ruler, a piece of paper, a pair of scissors, and something to write with.

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Use the ruler to draw 5 squares in a row that are 1 in by 1 in.

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Cut them out.

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Cut off two squares and draw a line diagonally across them.

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Do this again with a second pair of squares. Cut along the diagonals so that you have 1 square and 4 triangles.

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Using these five shapes see if you can create a square. I’ll post the answer in a few days 🙂 You can also leave your answer in the comments.

The idea for this came from Shapes in Math, Science and Nature.

Enigma Cafe

One of my favorite exhibits at the MoMath was the Enigma Cafe. There is no food or coffee, instead at each table there is some type of brain teaser or puzzle. I sat down at a Tangrams table, got frustrated, and immediately started scanning the room from something easier.

horseshoe puzzle

Ok, now I was feeling good. My Grandpa taught me how to solve that one.

Rubik's_Cube

Errr….

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So then I stopped solving and decided to just observe everyone else. What was really fascinating about the cafe was listening to the conversations. You could hear parents talking things through with their child or see two strangers bond over trying to eliminate one of the possibilities.

If you’d like to imitate the Enigma Cafe experience grab a friend and create your own tangrams. Then start puzzling away. An added benefit of exercising your brain is it will make you a better mathematician.

How to Seem Smarter Than You Are…A Math Trick That Will Impress Your Friends

We’ve all been jealous of the math whiz who can compute everything in their head and has buzzed in the answer before we can even read the question.  But what if you could be that person?  How would you like to wow the college class (or co-op group) on that first day with your incredible mental abilities?

What follows is a mental math trick that will allow you to square numbers in a matter of seconds.  Read through the steps…practice a few times…and then call over a parent and get ready to wow them!

Step 1: Ask your friend (parent, grandparent, etc.) to pick a number for you to square.

ex. 84

Step 2: Find the number d that is the difference between the number they picked and the nearest multiple of 10.

In this case it would be 4 because 84-80=4.

Step 3: In your head multiply (x+d) and (x-d) where x is the number they picked.  It isn’t as hard as you think because one of those numbers will be a multiply of 10.

(84+4)*(84-4)=(88)*(80)

In my head I do 8*88 and then add a zero on at the end.  I get 704 so add the zero and you have 7040.

Step 4: Take your result and add d squared.

7040+16=7056

It takes a little practice, but it is so impressive once you have the hang of it 🙂

Bonus: For those of you who are true math enthusiasts…can you figure out why this works?