Exponential Decay: Equations & Factors in Real Life

A radioactive substance has a half-life of 5 years. If you start with 80 grams, how much will remain after 15 years? Write the decay equation and identify the decay factor.

• 5 grams

• 10 grams

• 40 grams

• 20 grams

A car's value decreases by 20% each year. If the car is currently worth $15,000, what will its value be after 3 years? Write the decay equation and identify the decay factor.

• $8,400

• $10,000

• $7,680

• $9,600

A certain type of tree loses 25% of its leaves each autumn. If a tree has 200 leaves at the start of autumn, how many leaves will it have left after one autumn? Write the decay equation and identify the decay factor.

• 175

• 50

• 150

• 100

A certain medication in the bloodstream decreases by 15% every hour. If the initial amount is 200 mg, how much will be left after 6 hours? Write the decay equation and identify the decay factor.

• 90 mg

• 75.4 mg

• 100 mg

• 60 mg

A car depreciates in value by 18% each year. If the car was purchased for $20,000, what will its value be after 2 years? Write the decay equation and identify the decay factor.

• $15,000.00

• $10,000.00

• $18,000.00

• $13,448.00

A certain species of fish in a lake decreases by 10% each year due to overfishing. If there are 5,000 fish initially, how many will be left after 5 years? Write the decay equation and identify the decay factor.

• 3500

• 2500

• 2952

• 4000

A light bulb's brightness decreases by 40% every year. If the initial brightness is 1000 lumens, what will it be after 3 years? Write the decay equation and identify the decay factor.

• 216 lumens

• 1000 lumens

• 400 lumens

• 800 lumens

A certain type of plant loses 50% of its height each year due to drought. If a plant is initially 120 cm tall, how tall will it be after 2 years? Write the decay equation and identify the decay factor.

• 30 cm

• 90 cm

• 60 cm

• 15 cm

A certain chemical in a lab decays at a rate of 25% per hour. If you start with 400 grams, how much will remain after 3 hours? Write the decay equation and identify the decay factor.

• 100 grams

• 300 grams

• 168.75 grams

• 200 grams