Activities: The Envelope Trick

Teach your kid math magic that'll amaze you!

Submitted by
Sonam Adinolf

This magical, mathematical prediction trick will have your family and your kid's friends wondering, "How the heck did he do that?" (And there's a good chance even your kid won't be able to explain his secret!)

Little Houdini:
Your kid.
Volunteer:
Your kid's audience.
A "magic envelope":
Just a plain old envelope will do the trick. (No pun intended!)
A pen
A piece of paper

With his audience giving him rapt attention, have your kid secretly write down the four-digit number that is double the current year. (For example, if it's 2007, he'd write 4014.)
Have him put the paper in a blank envelope and seal it.
Then get your kid to ask for a volunteer. (Even if it is an audience of one—asking for a volunteer makes the trick official!)
Have him ask the volunteer to write down the following four numbers on a blank piece of paper:
- The year she was born.
- The year of a significant event in her life (i.e., the year she started middle school, or the year she discovered her first gray hair—it all depends on the audience).
- Her age. (In whole numbers, she can't say she's "10-and-a-half" or "30 and holding" or else the trick won't work.)
- The number of years that have passed since the important event.
Have the volunteer total the numbers. (Help or check her math to be sure it's correct.)
When the volunteer has her number, have your kid open his envelope. Presto! The number he wrote down will be the same as the number the volunteer came up with! How? It's magic!