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Suppose the number of potassium-40 atoms in a mineral can be modeled using 100 pennies.

Half-life Number of pennies
0 100
1st 50
2nd 25
3rd ?
How many atoms will there most likely be at the third half-life of potassium-40 in this model?



A model rock layer had 50 pennies (atoms of potassium-40).

How old is the rock layer?