COURSES Listen Question 1 Suppose a radioactive substance decays at a rate of $4 \%$ per hour. Question 2 How long does it take until the substance is half of its oriainal weight?

Step 1 ：Suppose a radioactive substance decays at a rate of $4 \%$ per hour.

Step 2 ：How long does it take until the substance is half of its original weight?

Step 3 ：Use the formula for exponential decay: \(final\_amount = initial\_amount \times (1 - decay\_rate)^{time}\)

Step 4 ：Set up the equation: \(0.5 \times initial\_amount = initial\_amount \times (1 - 0.04)^{time}\)

Step 5 ：Solve for time: \(time \approx 16.98\)

Step 6 ：\(\boxed{16.98}\) hours for the substance to decay to half of its original weight.