AP CSA 2.2 FRQ Practice: Range Checks

Unit 2: Selection and Iteration · Lesson 2.2 · FRQ Practice

Range Checks

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 2.2 pageAll Unit 2 lessons

Why this question is worth four points

A boolean method has only two possible answers, which makes it the easiest kind of method to get accidentally right. Every part here is checked from both sides, because a method that always returns true is correct on half the inputs and worth no points.

What you are given

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

The question

  1. (a) public static boolean isPositive(int n) returns whether n is greater than zero.
  2. (b) public static boolean inRange(int n, int low, int high) returns whether n is between low and high, inclusive of both.
  3. (c) public static boolean isMultiple(int n, int factor) returns whether n divides evenly by factor. Assume factor is not zero.
  4. (d) public static boolean sameParity(int a, int b) returns whether a and b are both even or both odd.

What the reader is looking for

  1. Write class Checks with the four static methods exactly as described. No main method.
  2. None of these needs an if statement. A comparison already IS a boolean, so return the comparison itself.
  3. Part (b) is inclusive at both ends. low and high are each inside the range.

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
5 1 10 5 7
Example 1 output
true
true
true
true
Example 2 input
1 1 10 3 4
Example 2 output
true
true
false
false

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
if (x > 0) { return true; } else { return false; } is the long way of writing return x > 0. Both are correct; only one of them is the point of this lesson.

    
Hint 2
Inclusive means the endpoints count. Using > and < instead of >= and <= excludes exactly the two values most likely to be tested.

    
Hint 3
Two numbers have the same parity when both remainders match. Comparing a % 2 to b % 2 handles that in one expression without four separate cases.



  
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) always returns true
    • 
      
  • part (b) excludes the endpoints, using strict comparisons
    • 
      
  • part (d) always returns true
    • 
      
  • part (c) tests the remainder against 1 instead of 0
    • 
    

  


  
Where to go next

  

    Rework the Lesson 2.2 page
    Try the from-scratch exercise for this lesson
    Try the debugging exercise for this lesson
  


  
  






  

















  
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