Growth & Decay: Real-World Math Scenarios for 8th Graders

A bacteria culture doubles in size every 3 hours. If you start with 500 bacteria, how many will there be after 9 hours?

• 4000

• 2000

• 1000

• 3000

A certain radioactive substance has a half-life of 5 years. If you start with 80 grams, how much will remain after 15 years?

• 10 grams

• 20 grams

• 40 grams

• 5 grams

A tree grows at a rate of 2 feet per year. If the tree is currently 10 feet tall, how tall will it be in 5 years?

• 15 feet

• 25 feet

• 30 feet

• 20 feet

A population of rabbits decreases by 25% each year. If there are currently 200 rabbits, how many will be left after 2 years?

• 100

• 112

• 75

• 150

A car's value depreciates by 15% each year. If the car is worth $20,000 now, what will its value be after 3 years?

• $18,000

• $12,282.50

• $15,000

• $10,000

A certain plant species grows by 50% every month. If you have 4 plants, how many will you have after 3 months?

• 10

• 13

• 15

• 8

A radioactive isotope has a half-life of 10 days. If you start with 160 mg, how much will be left after 30 days?

• 80 mg

• 40 mg

• 20 mg

• 100 mg

A fish tank has 100 liters of water, and it loses 10% of its water volume each week due to evaporation. How much water will be left after 2 weeks?

• 70 liters

• 90 liters

• 81 liters

• 75 liters

A population of 1,000 fish decreases by 20% each year due to overfishing. How many fish will be left after 3 years?

• 512 fish

• 800 fish

• 600 fish

• 400 fish

A certain type of tree can grow 3 feet in the first year and then 1 foot each subsequent year. How tall will the tree be after 5 years if it starts at 2 feet?

• 10 feet

• 7 feet

• 9 feet

• 8 feet