By examining the cumulative frequencies in the histogram, we find that 24 choir students have performed in at least 3 concerts.
To determine the number of choir students who have performed in at least 3 concerts, we need to consider the cumulative frequency for concerts 3 and above. Looking at the histogram, the cumulative frequency is obtained by adding the frequencies for each category up to the desired one.
The cumulative frequency for 0-2 concerts is 8, for 3-5 concerts is 8 (previous cumulative) + 9 = 17, for 6-8 concerts is 17 + 4 = 21, and for 9-11 concerts is 21 + 3 = 24.
So, the total number of choir students who have performed in at least 3 concerts is 24.