When I was in business school I had a wonderful teacher Adam Brandenberger who wrote a book called Co-Opetition. The book is chock full of lessons on how to apply mathematical game theory to business.
In the book, I learned how to fairly divide things between two companies. But it also works for dividing things between my two kids without them getting upset (formally called Envy Free division). If you have kids, you know that this is a non-trivial problem. Let’s use the example of a cupcake. The most obvious thing is to split the cupcake in half and distribute the two equal pieces to the children. Of course, because you can never cut the cake directly in half, one of the kids is going to complain of unfairness.
The book explains a better way called I cut, you choose . One child (normally the older one who’s better with a knife) makes the cut and the other child gets to choose the one he prefers. This forces the cutter to create two pieces that are as close to as equal as possible because he knows that he’s going to get the piece that’s second best.
This worked well and inspired me to try other systemic solutions to child problems. Here’s the way I solve the problem of two kids sharing an iPhone (or iPad) when watching a movie. Normally the child who’s holding the iPhone will slowly and unconsciously move the phone closer to him, ignoring his sibling. Eventually, the phone gets so far away that I hear, “Hey, I can’t see the phone!”
I’ve been able to solve this problem by having each child have one hand on the phone. Instead of one child controlling the phone, they are sharing control of the phone. This imperceptible pulling between the two children tends to leave the phone nicely spaced between them. You’d think you’d have constant fighting between the two kids — and you do! But the fights are so small that neither kid noticies.