This is a classic brain teaser I learned in middle school (or “junior high school” where I grew up).
Let’s prove that:
Â Here’s the proof:
Let’s start by establishing some variables:
Okay, so if that’s true, then we know:
Â In algebra, we learned we could multiply both sides of the equation, so:
Now, we can factor that equation to get:
Of course, cancels out, so:
Putting back in the numbers, we see that:
And there is our proof!
To misquote Groucho Marx:
“An eighth grader could understand that! Someone fetch me an eighth grader!”