The Handshake Problem!
This classic problem continues to stump people today. There's more than one way to figure this problem out, however, as the number of people increase, it's much more helpful to know and understand the algorithm.
You are in a roomful of 35 people. Everyone is asked to shake hands with everyone. How many handshakes will there be? How can you figure this out? What strategies will you use?
More problems of the week. When giving students problems like this one to solve, it's important to let them develop their own strategies to solve the problem. Some students will need to act it out, others will draw a diagram or use charts and then some may even try to develop the algorithm. Students should be provided with any types of math manipulatives they need when brainstorming their solutions.