Question

After two half-lives, a sample contains 10 grams of daughter isotopes. How many grams of the parent isotope were present to start?
Answer







60








20








40








30

@Earth Science

Answer 1

it is quartered so 40 g

Answer 2

I forgot the precise equation to determine half-lives, but yeah the answer is 40g

You began with x grams, and x * 0.5 grams after one half-life, and x * 0.5 * 0.5 = x * 0.25 grams after 2 half-lives. To get that x back, simply multiply what you have after the second half-live by 4 :-P