Hi Jenny.

Percentage of what? A percentage is a percentage of something.

About the only two things we can say about these numbers is that 29990 is 93.75% of 31990 and 31190 is 106.67% of 29990.

For example, if the original price of a car is $31990 and you bargain with the seller down to an agreed price of $29990, then you have reduced the original price by 6.25% (that's 100% - 93.75%).

If two competing car dealers, Cathryn and Chelsea, sell the same car and Cathryn sells for $31990 and the Chelsea sells for $29990, then you can say that Cathryn sells it for 6.67% more than Chelsea and Chelsea sells it for 6.25% less than Cathryn.

We only can say this because there is an implication within the English sentences which answers the "what" in "Percentage of what?"

When we say Cathryn sells it for 6.67% more than Chelsea, we mean Cathryn's extra amount is 6.67% of Chelsea's price.

There is context within the english sentence in this case. When you ask the question "What is the difference in percentage between 31990 and 29990?" there is not enough context in the question to understand what should be a percentage of what.

I hope this helps your understanding of percentages,
Stephen.