This dissertation investigates people’s numeric judgments and decisions (e.g., probability estimation and quantity selection). The first chapter examines whether having a choice increases people’s subjective probability of success. Previous research suggests that choice makes people feel more likely to achieve preferable outcomes, even when they are selecting among options that are functionally identical (i.e., choice causes an illusion of control). This notion has been widely accepted as evidence that choice can have significant welfare effects, even when it confers no actual control. However, a series of studies in this chapter shows that choice rarely makes people feel more likely to achieve preferable outcomes—unless it makes the preferable outcomes actually more likely—and when it does, it is not because choice causes an illusion, but because choice reflects some participants’ pre-existing (illusory) beliefs that the functionally identical options are not identical. The second chapter examines whether people have the tendency to choose a certain class of numbers more frequently in quantity decisions (e.g., choosing how many units of an item to acquire or consume). Previous research suggests that people often choose one or multiples of five and ten as focal numbers when selecting quantities. Studies in this chapter show that even numbers constitute another class of focal numbers, i.e., people are more likely to choose even numbers than odd numbers across a variety of quantity decisions, even excluding multiples of ten. This tendency attenuates when people can fluently retrieve an odd focal number (e.g., one unit per person) or fluently process an odd number (e.g., nine units organized in a three-by-three array). Overall, this dissertation aims to improve an understanding of people’s numeric judgments and decisions.