Tag Archives: math trick

Good Square Root Trick for your students

1 Sep

While in Las Vegas this past summer, I was in a magic shop, and picked up the book “Self-working Number Magic” by Karl Fulves. It has all kinds of fun number tricks to play with (on) your students. One puzzle that gave me pause was this one:

During a class discussion on square roots, Johnny wrote this equation on the board.          square-root

It was obviously wrong, and the teacher was about to cross it out, but on second thought it looked almost right.  Is the equation correct? Almost correct? Or is it completely wrong?

Here is the answer.