500
Connor had 20 balloons at his birthday party. 1/4 of the balloons were red, 1/10 of the balloons were green, and the rest were blue. How many blue balloons were at the party?
1/4 = 5/20, so there were 5 red balloons.
1/10 = 2/20, so there were 2 green balloons.
20 - 5 - 2 = 13
Connor had 13 blue balloons.