As you're doing these, think of which one you'd like to present in class, and let me know as soon as you've decided.
Here's a silly way to sort a bunch of numbers: generate each of the possible permutations of the numbers, and for each one, test whether it's in order.
Analyze this algorithm: tell how long it takes, as a function of how many numbers there are, using big-O notation.
You are given a bunch of floating-point numbers, and you want to find which two of them are closest together. Describe an algorithm (in pseudocode, as efficient as you can) that solves this problem. Analyze the algorithm: tell how long it will take, as a function of how many numbers there are.