Solution: If there are X boys and 98-x girls in the class, we can get:

x-x/ 10=98-x-3

The solution is x=50.

So * * * there are 50 boys and 48 girls.

Analysis: Total number of boys+total number of girls =98.

Total number of boys-number of boys participating in the competition = total number of girls-number of girls participating in the competition (3)

Suggestion: It is very useful to do this kind of problems mainly by grasping the equivalence relationship!