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.

   Bo's plant grows the same amount each week: 12 cm at week 0 and 27 cm at week 3. What model gives the height y after x weeks?

   y = 5x + 12
2. 2.

   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
3. 3.

   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
4. 4.

   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
5. 5.

   Noah reads that a village of 800 people grows by 3% a year. What model gives the people y after x years?

   y = 800(1.03)^x
6. 6.

   Pia's chess club has 40 members and grows by 25% each month for a while. What model gives the members y after x months?

   y = 40(1.25)^x
7. 7.

   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
8. 8.

   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
9. 9.

   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 ≤ 20
   • 0 ≤ x ≤ 10
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
    • x ≥ 0
    • 0 ≤ x ≤ 56