A certain radioactive substance decays at a rate of 10% per hour. If you start with 200 grams, how much will remain after 3 hours?

✓ Correct Answer: Option B

The formula for decay is A = P(1 - r)^t. Substituting P=200, r=0.10, t=3: A = 200(1 - 0.10)³ = 200(0.9)³ = 200(0.729) = 145.8 grams.