I’m studying for my Mathematics class and don’t understand how to answer this. Can you help me study?

What are Bond Ratings and How Do They Impact Bond Valuation?

Your postings should be qualitative and provide substantive depth that advances the discussion.

Who are the bond ratings agencies and what do the ratings mean? When ratings fall what happens to the valuation of a bond and why? Cite a reference to support your answer. Give an example of an economic event that could cause bond ratings to change. Tell why the change in ratings would occur.