AP CSA 3.1 FRQ Practice: One Place for Each Fact

Unit 3: Class Creation · Lesson 3.1 · FRQ Practice

One Place for Each Fact

A free response question in the shape the exam uses: a stated contract, four rubric parts, and no main method handed to you. Worth 4 points.

Back to the Lesson 3.1 pageAll Unit 3 lessons

Why this question is worth four points

Abstraction on the exam means the caller does not get to know how you stored anything. This class is asked for two facts that are really one: a total and a count. Store both and they will disagree the first time something changes; store the ingredients and compute the rest, and they cannot.

What you are given

Nothing is given. Write a class named Tally. Do not write a main method: a hidden driver constructs your object, calls its methods, and prints what it observes.

The question

  1. (a) A constructor Tally() that starts with nothing recorded.
  2. (b) public void add(int value) records one more value.
  3. (c) public int getCount() returns how many values have been recorded, and public int getTotal() returns their sum.
  4. (d) public int getAverage() returns the total divided by the count using integer division, and 0 when nothing has been recorded.

What the reader is looking for

  1. Write class Tally with the constructor and methods described. No main method.
  2. Part (d) must not divide by zero. A Tally with nothing in it returns 0 rather than crashing.
  3. Do not store the average. It is computed from the total and the count, and a stored copy is a third fact that can disagree with the other two.

Worked examples

These show what a correct answer prints. There are more cases you cannot see, and they use different values, so an answer built around just these numbers will fail.

Example 1 input
4
10 20 30 41
Example 1 output
0
0
4
101
25
Example 2 input
1
7
Example 2 output
0
0
1
7
7

Your answer

Main.java

Input for the Run button

How this is scored: your answer runs against every test case, and the fraction it passes becomes your score out of 4. That is not how a human AP reader marks a rubric, so treat the score as a check on whether your code works, and the rubric above as the thing you are actually practising.


  

  
Stuck?

    
Hint 1
The driver builds an EMPTY Tally first and asks it for an average. If your getAverage divides without checking, that call throws ArithmeticException before anything else is printed.

    
Hint 2
add changes two fields at once. Forgetting to increment the count gives a total that looks right and an average that is wildly wrong, with no error message.

    
Hint 3
Integer division is what the question asks for. 7 / 2 is 3, and no rounding is wanted.



  
Before you submit

  
3 mistake(s) that lose points on this question
    
Each of these is a real error the grader catches. Check your answer against them before you submit, not instead of trying.

    
    
      
  • getAverage divides without guarding the empty case, so an empty Tally throws
    • 
      
  • add forgets to increment the count
    • 
      
  • add counts but never accumulates the total
    • 
    

  


  
Where to go next

  

    Rework the Lesson 3.1 page
    Try the from-scratch exercise for this lesson
    Try the debugging exercise for this lesson
  


  
  






  

















  
Get in Touch

  
Whether you're a student, parent, or teacher — I'd love to hear from you.







  
Just want free AP CS resources?

  

    Enter your email below and check the subscribe box — no message needed.
    Students get daily practice questions and study tips. Teachers get curriculum resources and teaching strategies.
  







  
  Typically responds within 24 hours






  
✓

  
Message Sent!

  

    Thanks for reaching out. I'll get back to you within 24 hours.
  







  


  

    
    

    
    

      

        
        
      

      

        
        
      

    


    
    

      

        
        
      

      

        
        
      

    


    
    

      

        
        
      

      

        
        
      

    


    
    

      
🏫 Welcome, fellow educator!

      

        I offer curriculum resources, practice materials, and study guides designed for AP CS teachers.
        Let me know what you're looking for — whether it's classroom materials, a guest speaker,
        or Teachers Pay Teachers resources.
      

    


    
    

      
      
    


    
    

    
    

      
    

  







  

    ✉
    
Email

    
[email protected]

  

  

    📚
    
Courses

    
AP CSA, CSP, & Cybersecurity

  

  

    ⏱
    
Response Time

    
Within 24 hours

  







  Prefer email? Reach me directly at
  [email protected]