For ratio questions, add the numbers on each side and use that as a denominator to find fractions:
If the ratio of girls to boys is 3:2, 3+2=5, so 2/5 of students in the 8th grade are boys. 2/5 can be written as 40/100 if you multiply both the numerator and denominator by 20, and 40/100 is 40%. Therefore, the answer is B.
