Build a linear or exponential model, and say what the numbers mean

Answer Key - Grade 9 Math Worksheet

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

1. 1.

   Jun's class pencil bin loses the same number each day: 90 pencils at day 0 and 60 at day 5. What model gives the pencils y after x days?

   y = 90 − 6x
2. 2.

   Kira's science video shows duckweed multiplying by the same factor each week: 4 cm² at week 0 and 36 cm² at week 2. What model gives the area y after x weeks?

   y = 4(3)^x
3. 3.

   Luz's class phone tree multiplies by the same factor each round: 5 people at round 0 and 80 at round 2. What model gives the people y in round x?

   y = 5(4)^x
4. 4.

   Milo's class keeps a pretend fund of $500 that earns 4% interest a year, compounded yearly. What model gives the balance y after x years?

   y = 500(1.04)^x
5. 5.

   Ren's play ball first rebounds 100 cm (bounce 0). Each bounce is 20% lower than the one before. What model gives the height y of bounce x?

   y = 100(0.8)^x
6. 6.

   After a cleanup, algae in Tala's school pond covers 900 m² and shrinks by 30% each week. What model gives the area y after x weeks?

   y = 900(0.7)^x
7. 7.

   Zee's 600 mL water bottle drains 40 mL a minute, so y = 600 − 40x mL are left after x minutes. Which inputs x make sense?

   • 0 ≤ x ≤ 15
   • x ≥ 0
   • 0 ≤ x ≤ 600
8. 8.

   Ari's 20 cm candle burns 2 cm an hour, so y = 20 − 2x cm are left after x hours. Which inputs x make sense?

   • x ≥ 0
   • 0 ≤ x ≤ 10
   • 0 ≤ x ≤ 20
9. 9.

   Bo's class trip fund has $180 and spends $15 a day, so y = 180 − 15x dollars are left after x days. Which inputs x make sense?

   • x ≥ 0
   • 0 ≤ x ≤ 180
   • 0 ≤ x ≤ 12
10. 10.

    Esme's 56-page sticker book gets 4 pages filled a day, so y = 4x pages are full after x days. Which inputs x make sense?

    • 0 ≤ x ≤ 14
    • 0 ≤ x ≤ 56
    • x ≥ 0