Guess the Number

Guess the secret number like a Magician, or even better like Mathematician!

So, what are the rules of this game? 

In order to play this game you will need a partner, someone from your family or a friend. You can ask them to think of a number, their secret number, which will be your goal to guess. 

After that, ask them to:

Subtract 11

Add  2

Aaaand, then they should tell you the result the have got.

 So, let's say they have got 5. What should you do to find out the mysterious number?

Credit: http://clipart-library.com/magic-hat.html

The "secret recipe" is to Work backward to find the original number: 😉

We should start with the 5, then apply every opposite operation of the stated one. So, opposite of addition is subtraction, hence, we should do

 5 -2, which equals 3, 

then taking that (5-2) and instead of subtraction, again applying the opposite operation, we are going to do addition, we will get

(5-2)+11=14,

 and voilà, the number that you need is 14. 

You can tell your partner the number, and I believe he /she will be super-surprised by your magical skills, which are actually mathematical skills 😊

Credit:Bitmoji App

The Math Behind 

This is an example of a grade 7 problem, when the students are working on the concepts of Operations with Integers. 

But, absolutely we can make it to a G4-level, just using smaller numbers, where the students will be able to do the math by using only logical reasoning, since they haven't learned the theory of negative numbers. Or, even G11-level, if we add some exponents, or maybe irrational numbers, logarithm's conditions and so on.

Let's present the Math behind the example given above.

This is nothing more than solving an (in this case linear) equation with one variable, let's denote x. 

(x-11)+2=14 

x-11+2=14 

x+9=14, 

x=14-9 

x=5 

As you can see, math can be hiding anywhere around us 😊 Even in a wizard's hat 🧙