The Wall Street Journal reported that the spread on a bond issued by Citigroup changed by 50 basis points (100 basis points = 1%) during trading on December 7.

a. The Citigroup bond was included on the list of bonds having spreads that tightened the most. In general, what would cause a bonds spread to tighten?

b. Explain how the tightening of a bonds spread would affect the bonds value.