Is it a function? Inputs, outputs, domain and range

Answer Key - Grade 8 Math Worksheet

Circle the best answer, or write your answer on the line.

1. 1.

   Bo copies a mapping from the board, using a very long ruler for the arrows. Is it a function, and why?

   • No: inputs -2 and 2 both send an arrow to 3
   • Yes: no two arrows land on the same output
   • Yes: inputs -2, -1, 1, 2 and 4 each send one arrow
2. 2.

   (5, -1), (-3, 4), (0, 6), (5, 2), (2, 4). Kira writes clue points for a grid game, and two clues fight over input 5. Is it a function, and why?

   • No: input 5 has two outputs, -1 and 2
   • No: inputs -3 and 2 share the output 4
   • Yes: inputs -3, 0, 2 and 5 each have an output
3. 3.

   Luz writes (temperature in °C, layers worn) on winter walks. At -6°C even the scarf wears a scarf. Is it a function, and why?

   • Yes: inputs -6, -1, 2 and 7 each have one output
   • Yes: no output appears twice, so no layer count repeats
   • No: inputs -1 and 2 share the output 3
4. 4.

   In a video game level, Pia plots where four stars sit on the grid. Is it a function, and why?

   • No: the points are not on one straight line
   • Yes: inputs -4, -2, 1 and 3 each have one point
   • Yes: the points are evenly spaced along the grid
5. 5.

   Ren's weather log: Monday 64°F, Tuesday 70°F, Thursday 64°F. Input: temperature. Output: the day. Is it a function, and why?

   • Yes: every temperature has a day
   • No: Wednesday is missing, so the log is not complete
   • No: 64°F goes with two days, Monday and Thursday
6. 6.

   Tala times a 200 m race: lane 2 runs 38 seconds, lane 4 runs 41 and lane 5 runs 38. Input: lane. Output: time. Is it a function, and why?

   • Yes: each lane has just one time
   • Yes: no time appears twice
   • No: lanes 2 and 5 share a time
7. 7.

   In Zee's bike rack, bike 3 has 7 gears, bike 8 has 21 and bike 12 has 7. Input: bike number. Output: gears. Is it a function, and why?

   • Yes: each bike has just one gear count
   • Yes: no gear count appears twice
   • No: bikes 3 and 12 share a gear count
8. 8.

   (-5, 2), (0, 7), (4, 2), (-2, 1), (6, 3). Bo lists points for a grid drawing of a sailboat. What is the domain (all the inputs)? List each value once.

   -5, -2, 0, 4, 6

9. Read this first

   Use the table

   input: x	output: y
   3	8
   6	5
   1	8
   6	2
   9	4

10. 9.

    Jun checks a classmate's table in math club. This table is not a function. Which input has two different outputs?

    6
11. 10.

    Milo prints a 12-page comic. The more pages, the longer the printing takes. Which amount is the input (independent variable)?

    • The input is the printing time
    • The input is the number of pages
    • The input is the printer