A greedy algorithm works if a problem exhibits the following two properties:

1. Greedy Choice Property: A globally optimal solution can be reached at by creating a locally optimal solution. In other words, an optimal solution can be obtained by creating "greedy" choices.
2. Optimal substructure: Optimal solutions contain optimal subsolutions. In other words, answers to subproblems of an optimal solution are optimal.

Example:

1. machine scheduling
2. Fractional Knapsack Problem
3. Minimum Spanning Tree
4. Huffman Code
5. Job Sequencing
6. Activity Selection Problem