Try this trick
a few times, and you'll realize that it doesn't matter what numbers
you or your friend choose. The trick works no matter what.
Here's why.
In a twodigit number, the first number (the number on the left)
counts the number of sets of 10—the 10’s place—and
the second number (the number on the right) counts the number of
1’s—the 1’s place. The number 38, for example, has
three 10’s and eight 1’s.
All the math
you told your friend to do was just a roundabout way of putting
your friend's chosen number in the 10’s place and your number
in the 1’s place.
To see what's
really going on, let's go through the steps, one at a time.
Because it doesn’t
matter what number your friend chooses, we’ll just represent
it with a symbol, a .
This triangle could be any number between 1 and 9.
First, you told
your friend to double his or her number. That’s two times his
number, or two times .
You can write it mathematically like this:
