A rock sample containing an isotope with a half-life of 28 million years has an initial mass of 184 grams. How much parent isotope remains after 3 half-lives?
A) 23 grams
B) 46 grams
C) 69 grams
D) 115 grams
E) 161 grams

Question

Quizplus · Accepted Answer

After 3 half-lives, the mass of the parent isotope remaining is 1/8 of the initial mass (since each half-life halves the remaining amount). Therefore, 184 grams / 8 = 23 grams.

A Rock Sample Containing an Isotope with a Half-Life of 28