Answer:
is the fraction of 8th graders who are boys.
Step-by-step explanation:
Let total number of 8th graders = 
Given that,
of 8th graders play sports
8th graders who play sports = 
Also, Given that,
of 8th graders that play sports are boys
Number of 8th graders that play sports, and are boys = 
Hence, the answer is:
is the fraction of 8th graders who are boys.