Geometry

Question Analysis
This question involves combining data from two frequency tables to calculate a probability.
The main focus is on correctly adding up the relevant frequencies from both tables for the desired category (grade B) and also finding the total combined frequency of all students in both classes to calculate the probability.

Key Concept Explanation
Probability of an event is .
When combining data from multiple sources (in this case, two frequency tables), we sum up the relevant frequencies and the total frequencies across all the tables.

Step-by-Step Solution
First, find the total number of students in Class A: