AP CSA 1.5 FRQ Practice: Fuel Economy Report

Unit 1: Using Objects and Methods · Lesson 1.5 · FRQ Practice

Fuel Economy Report

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 1.5 pageAll Unit 1 lessons

Why this question is worth four points

Casting is the single most reliable place to lose an FRQ point, because the wrong answer looks right. (double) (a / b) casts AFTER the integer division has already thrown the fraction away. This question asks for the same quotient three different ways so the difference is on the page.

What you are given

Two variables are declared and assigned for you: int miles and int gallons.

The question

  1. (a) Print miles per gallon using integer division, so the fraction is discarded.
  2. (b) Print miles per gallon as an exact double.
  3. (c) Print the miles left over that the whole number in part (a) does not account for.
  4. (d) Print the exact result from part (b) rounded down to an int by casting.

What the reader is looking for

  1. Write a code segment that prints four lines in rubric order.
  2. Part (b) must cast BEFORE the division, not after. Casting the result of int division is too late.
  3. Part (c) is the remainder operator. Part (d) is a cast applied to the double from part (b).

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 miles = 250;
int gallons = 8;
Example 1 output
31
31.25
2
31
Example 2 is given
int miles = 300;
int gallons = 10;
Example 2 output
30
30.0
0
30

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
(double) miles / gallons casts miles first, so the division is double division. (double) (miles / gallons) divides as ints first and then converts the already truncated answer, which is the classic lost point.

    
Hint 2
The remainder operator % gives what is left after integer division. miles / gallons and miles % gallons together account for every mile.

    
Hint 3
Casting a double to an int truncates toward zero. It does not round: (int) 9.98 is 9.



  
Before you submit

  
2 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 (b) casts AFTER the integer division rather than before it
    • 
      
  • part (d) rounds instead of truncating
    • 
    

  


  
Where to go next

  

    Rework the Lesson 1.5 page
    Try the from-scratch exercise for this lesson
    Try the debugging exercise for this lesson
  


  
  






  

















  
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