AP CSA 1.8 FRQ Practice: Precondition Contract

Unit 1: Using Objects and Methods · Lesson 1.8 · FRQ Practice

Precondition Contract

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 1.8 pageAll Unit 1 lessons

Why this question is worth four points

Documentation on the exam is not a comment you write, it is a contract you are held to. A precondition tells you what you may ASSUME, and every point lost to "but what if the input is negative" is a point lost to code defending against a case the documentation already ruled out. This question states its preconditions and then scores whether you trusted them.

What you are given

Three variables are declared and assigned for you: int boxes, int perBox and int shipped. Preconditions: boxes is at least 1, perBox is at least 1, and shipped is between 0 and boxes * perBox inclusive.

The question

  1. (a) Print the total number of items across all boxes.
  2. (b) Print how many items are still unshipped.
  3. (c) Print the number of FULL boxes the unshipped items would fill.
  4. (d) Print the percentage shipped, truncated to a whole number.

What the reader is looking for

  1. Write a code segment that prints four lines in rubric order.
  2. The preconditions guarantee perBox is at least 1, so part (c) and part (d) never divide by zero. You do not need to check for it, and the exam does not award a point for checking.
  3. Part (d) is shipped * 100 / total, which truncates once at the end. Dividing first gives 0 every time.

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 is given
int boxes = 10;
int perBox = 12;
int shipped = 45;
Example 1 output
120
75
6
37
Example 2 is given
int boxes = 4;
int perBox = 25;
int shipped = 0;
Example 2 output
100
100
4
0

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
A precondition is a promise made TO you. You may assume perBox is at least 1 and write the division directly.

    
Hint 2
Part (c) asks for FULL boxes, which is what integer division already gives you. 7 items at 3 per box is 2 full boxes, not 2.33 and not 3.

    
Hint 3
Part (d) must multiply before it divides. shipped / total is 0 for every input where shipped is smaller than total, so multiplying that by 100 is still 0.



  
Before you submit

  
1 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.

    
    
      
  • part (d) divides before multiplying, so the percentage is always zero
    • 
    

  


  
Where to go next

  

    Rework the Lesson 1.8 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]