The Take a Penny Problem – addition through subtraction.
In The Take a Penny Problem, you begin with five pennies in your possession. You place them on a table. Doesn’t matter how; just lay them out.
Alright, you have five pennies – or five identical objects, preferably circular objects with a little weight. Once you’ve laid them out, arrange them to make two lines: place the first penny wherever you’d like, then place one beside it, then place another at a 90 degree angle, so that any pennies added to the row will never intersect with the other row. Now, place two pennies after the line along the x axis (horizontal) and then place one penny along the y (vertical) axis so that you have two rows of pennies. One row has three and one row has two.
The problem: with your pennies so laid out, you will have a row of three along the x axis and a row of two along the y axis. To solve the problem, you must make one move and create two rows of three. The proviso here is to assume that each penny is of equal value in adding or subtracting from the horizontal and vertical rows and that they retain the same value when they’re moved. As far as I know, this problem has a simple solution. Despite this, I’ve put this question to dozens of people, students, friends, and unwitting family members.
Now, with one move you are to create two rows of three, the in a row on each axis, If you can’t figure it out, click here for the resolution.