Comparison of Student Preferences for Class Types

A school conducted a survey to find out how many students prefer online classes versus in-person classes. The survey results are as follows:

• 30 students prefer online classes.
• 20 students prefer in-person classes.
• 50 students did not express a preference.

Based on these results, answer the following questions:

Quantity A: The number of students who prefer online classes.

Quantity B: The number of students who prefer in-person classes.