Final answer:
To determine the grams of the parent isotope in the original sample, we can use the formula and solve for the initial amount.
Step-by-step explanation:
To determine how many grams of the parent isotope were in the original sample, we need to understand that the quantity of the parent isotope decreases by half after each half-life. In this case, after one half-life, 20g of the parent isotope remains.
We can use the formula:
Remaining amount = Initial amount * (1/2)^(number of half-lives)
Substituting the values, we have:
20g = Initial amount * (1/2)^1
Simplifying, we find that the initial amount is:
Initial amount = 20g * 2 = 40g
Therefore, there were 40 grams of the parent isotope in the original sample.