Large numbers play a significant role in personal and political financial choices and the understanding of exponentialgrowth. Large numbers are also often misjudged, showing a logarithmic number understanding. Small numbers are how-ever represented in a linear fashion, due to direct experience on for example number lines. Earlier, it was shown that largenumber comprehension can be trained, influencing societally relevant choices. We trained large number comprehensionusing a serious game (RunTheLine): an infinite runner game where an avatar runs on a number line ranging till one billion.Due to the game mechanics, the players walk the number line at both small and large numbers in small steps, making themaware of the continuity of the number line. Pre-post test differences show a change in economic judgments compared toa control group. This offers a scientific manipulation of behavioral and cortical number line representations and potentialeducational applications.