The game is pretty simple – one person thinks of a number between 1 and 99 and the other person comes up with the number that will add to that number to make 100. Warming up we start with numbers like 30, 45, 75 etc. Then we move on to more difficult numbers like 37. Many students will think first that 73 is the matching pair. This is because they want to make 100 and they know that 30 and 70 go together. When I explained ninety-ten, the problem became much easier. They were now trying to make nine tens, so 63 was immediately identified.
Sometimes we need to think about numbers a little differently. From place value to working from left to right, there is much more freedom in math than we’ve been led to believe. Create something new!