Suppose the tree diagram below represents all the students in a high school and that one of these students were chosen at random. if the student is known to be a girl, what is the probability that the student is right-handed?

The question is: If the student is known to be the girl (300 girls) what is the probability of being right handed.

We know that there are 300 girls, and that out of those 300, there are 250 girls right handed. 

Divide 250 with 300

250/300 = 0.83333, or 83.33%

0.83333, or 83.33% is your answer

hope this helps