Question

the half - life of a particular radioactive substance is 1 week. if you started with 70 grams of this substance, how much of it would remain after 3 weeks? remaining amount =? (1 - )^ remaining amount = i(1 - r)^t enter the number that belongs in the green box.

Explanation:

Step1: Identify the initial amount

The initial amount $I$ of the radioactive - substance is 70 grams. This is the value that goes in the green box in the formula $Remaining\ Amount = I(1 - r)^t$.
70

Step2: Identify the decay rate

The half - life is 1 week. In one half - life, half of the substance decays. So the decay rate $r=\frac{1}{2}$.

Step3: Identify the number of time periods

The time elapsed $t$ is 3 weeks. Since the half - life is 1 week, the number of half - lives (time periods) is 3.

Answer:

70