Exponential growth and decay

Answer Key - Grade 9 Math Worksheet - Challenge Me

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

1. 1.

   Noah's town grows 10% each year. One long arrow in the growth table jumps from year 0 to year 2. What number goes on that long arrow?

   1.21
2. 2.

   Pia's robotics club grows 20% each year. One long arrow in the growth table jumps from year 0 to year 2. What number goes on that long arrow?

   1.44
3. 3.

   A used bike's value drops 10% each year, and Ren tracks it. One long arrow in the growth table jumps from year 0 to year 2. What number goes on that long arrow?

   0.81
4. 4.

   Tala's pond plant patch grows 50% each year. One long arrow in the growth table jumps from year 0 to year 3. What number goes on that long arrow?

   3.375
5. 5.

   A lab has 400 mg of iodine-131, whose half-life is about 8 days. Bo reads the label. About how many mg are left after 32 days?

   25
6. 6.

   A lab sample has 160 mg of technetium-99m, whose half-life is about 6 hours. Esme reads the label. About how many mg are left after 24 hours?

   10
7. 7.

   A lab makes 3200 mg of carbon-11, whose half-life is about 20 minutes. Jun reads the label. About how many mg are left after 80 minutes?

   200
8. 8.

   Town A has 8,000 people growing 1% a year. Town B has 3,000 growing 9% a year. Luz compares them. Which is bigger after 5 years?

   • Town A
   • They are equal
   • Town B
9. 9.

   Lab sample A has 1,200 mg and loses 10% a day. Sample B has 900 mg and loses 2% a day. Milo compares them. Which is bigger after 4 days?

   • They are equal
   • Sample B
   • Sample A
10. 10.

    Fern patch A covers 600 square cm, growing 20% a week. Patch B covers 2,000, growing 5% a week. Noah compares them. Which is bigger after 6 weeks?

    • They are equal
    • Patch A
    • Patch B