Answer to Question 1
The Parent+Daughter=Total, so 2000+30000 = 32000
P D HL
32000 0 0
16000 16000 1
8000 24000 2
4000 28,000 3
2,000 30,000 4
4 x 1by = 4 billion years old
The answer is 4 half-lives have gone by; the age of the rock is 4 billion years old.
Answer to Question 2
Cretaceous, because the conglomerate contains a Cretaceous fossil. Note: Many students will conclude a Triassic age, based on the age of the cobble (sample A). This is an important opportunity to link conceptual understanding of rock-dating methods to the rock cycle.