Question

The half-life of a radioactive substance is 3.6 days. How much of 20 mg of this radioactive substance will remain after 36 days.

• A. 0.0019 mg
• B. 1.019 mg
• C. 1.109 mg
• D. 0.019 mg

Answer 1

Answer: (D)

0.019 mg

Answer 2

$M = M_{0}\left( \frac{1}{2} \right)^{\frac{t}{T_{1/2}}} = 20 \times \left( \frac{1}{2} \right)^{\frac{3.6}{3.6}} = 20 \times \left( \frac{1}{2} \right)^{10} = 0.019mg$.