 This is a mathematical snack from the Association of Teachers of Mathematics for you to enjoy. This video shows you how to play a simple game called NIM. It's a game for two players and we're going to have a game now and you can see how we play it. We start with some tally marks and we can have tally marks in as many rows as we want. I'm going to choose five there, four there, two there and one there. You can have as many rows as you want and you can have as many tally marks in any row that you choose. Anyway, we're going to take it in turns to cross out tally marks and the rule is this. You can cross out as many tally marks in any one row that you choose. The person who crosses out the last tally loses. Let's play. I'm going to cross out three. We're going to cross out two. I'm going to cross out one. I'm going to cross out the whole of that row. I'm going to cross out those two. I'm going to cross out that one. I'm crossing out the last one so I lose. Let's have another game. You can start this time. I'm going to take out those three tallies. I'm going to take out all of that row. I'm going to take out that one. I'm going to take out all of that row. I'm going to take out that one and lose. You've lost. So, with this activity, this is your task. Have fun.