AP CSA 2.3 FRQ Practice: Shipping Tiers

Unit 2: Selection and Iteration · Lesson 2.3 · FRQ Practice

Shipping Tiers

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 2.3 pageAll Unit 2 lessons

Why this question is worth four points

A tiered rule is the most common if question on the exam, and it has one trap: the order of the branches. Written from the loosest condition down, every input falls into the first branch and the rest are unreachable. The tiers here are arranged so that mistake changes the answer.

What you are given

Nothing is given. Write a class named Shipping containing exactly the four static methods described below. Do not write a main method.

The question

  1. (a) public static int fee(int weight) returns 5 when weight is under 10, 10 when weight is under 50, and 20 otherwise.
  2. (b) public static String size(int weight) returns "SMALL" under 10, "MEDIUM" under 50, and "LARGE" otherwise.
  3. (c) public static int discounted(int fee, boolean member) returns half the fee (integer division) for a member, and the full fee otherwise.
  4. (d) public static int total(int weight, boolean member) returns the discounted fee for that weight.

What the reader is looking for

  1. Write class Shipping with the four static methods exactly as described. No main method.
  2. Part (d) must call your own part (a) and part (c) rather than repeating their rules. A tier rule written twice is a tier rule that will disagree with itself later.
  3. "Under 10" means strictly less than 10. A weight of exactly 10 is in the middle tier.

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
3 true
Example 1 output
5
SMALL
50
2
Example 2 input
10 false
Example 2 output
10
MEDIUM
100
10

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
Check the tightest condition first. If you test weight < 50 before weight < 10, then a weight of 3 is under 50 and takes the middle tier, and the small tier can never be reached.

    
Hint 2
A boolean parameter does not need == true. if (member) is the whole condition.

    
Hint 3
Part (d) is one line if you reuse the methods you already wrote. Copying the tier rules into it is how the two versions drift apart when a price changes.



  
Before you submit

  
4 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 (a) tests the loosest tier first, making the small tier unreachable
    • 
      
  • part (b) uses <= at the tier boundary, so exactly 10 is SMALL
    • 
      
  • part (c) discounts non-members instead of members
    • 
      
  • part (d) ignores membership and returns the undiscounted fee
    • 
    

  


  
Where to go next

  

    Rework the Lesson 2.3 page
    Try the from-scratch exercise for this lesson
    Try the debugging exercise for this lesson
  


  
  






  

















  
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