75%
To determine the percentage of 6th graders who ran fewer than 28 laps, we need to look at the lower quartile, which is 13, and the median, which is 28. Since the lower quartile represents the 25th percentile and the median represents the 50th percentile, the percentage of 6th graders who ran fewer than 28 laps is 25% + 25% (since the lower quartile includes all of those who ran fewer than 28 laps) = 50%. Therefore, approximately 50% of 6th graders ran fewer than 28 laps.