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

Answer Key - Grade 8 Math Worksheet - Building Confidence

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

1. 1.

   Rows sorted by input so repeated inputs sit side by side. Bo writes each bus number and the length of its route in miles. Bus 7 passes twice, so it gets written twice. Is it a function, and why?

   • No: input 7 appears in two rows
   • Yes: no input appears twice, so no bus repeats
   • Yes: inputs 2, 7 and 9 each have one output

2. Read this first

   Use the table

   input: number typed in	output: number shown
   5	2
   3	8
   5	6
   1	4

3. 2.

   Jun's toy robot answers number questions, but it hiccups now and then. The table shows what went in and what came out. Is it a function, and why?

   • No: input 3 has two outputs, 8 and 4
   • Yes: inputs 1, 3 and 5 each have an output
   • No: input 5 has two outputs, 2 and 6
4. 3.

   Kira counts the stickers on each page of a sticker book. Page 1 has a shiny dragonfly. Is it a function, and why?

   • Yes: no output appears twice, so no count repeats
   • Yes: inputs 1, 2, 3 and 4 each have one output
   • No: inputs 3 and 4 share the output 6
5. 4.

   Noah weighs boxes for a move. Box 3 got weighed twice on a wobbly scale. The arrows go from box number to pounds. Is it a function, and why?

   • No: input 3 sends arrows to 6 and 9
   • No: input 1 sends arrows to 4 and 6
   • Yes: inputs 1, 3 and 5 each send an arrow
6. 5.

   Two friends count kites over the park each hour, and Bo plots both counts. At hour 3 they disagree. Is it a function, and why?

   • Yes: no two points are at the same height
   • No: the points do not start at (0, 0)
   • No: (3, 2) and (3, 7) are on one up-and-down line
7. 6.

   Esme plots (week, inches) for a bean sprout. It shot up in week 3, then slowed down. Is it a function, and why?

   • Yes: inputs 0, 2, 3 and 6 each have one point
   • No: the points are not on one straight line
   • Yes: the points are evenly spaced
8. 7.

   At camp, Jun hands out shirts: one 11-year-old gets M, a 12-year-old gets L, and another 11-year-old gets S. Input: age. Output: shirt size. Is it a function, and why?

   • No: age 11 goes with two sizes, M and S
   • Yes: every age has a shirt size
   • No: sizes are letters, not numbers
9. 8.

   Kira's reading log: 12 pages on Monday, 9 on Tuesday and 12 on Wednesday (the book got exciting). Input: day. Output: pages read. Is it a function, and why?

   • No: Monday and Wednesday share 12 pages
   • Yes: each day has just one page count
   • Yes: no page count appears twice
10. 9.

    Luz checks the lunch seats: ticket 4 sits at table 2, ticket 9 at table 5 and ticket 13 at table 2. Input: ticket. Output: table. Is it a function, and why?

    • Yes: each ticket has just one table
    • No: tickets 4 and 13 share table 2
    • Yes: no table number appears twice
11. 10.

    (1, 7), (2, 4), (4, 7), (5, 9). Noah plants sunflower seeds and writes (day, seeds sprouted). What is the range (all the outputs)? List each value once.

    4, 7, 9