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ConcepTest: What percentage of parent isotopes remain?

ConcepTest questions by David McConnell , David Steer , Walter Borowski, Jeffrey Dick, Annabelle Foos, Jeffrey Knott, Alvin Konigsberg, Michelle Malone, Heidi McGrew, Kathie Owens, and Stephen Van Horn


The half-life of a radioactive isotope is 1,000 million years. Scientists testing a rock sample discover that the ratio of parent and daughter isotopes indicates that the rock is 3,000 million years old. What percentage of parent isotopes remain in the sample?

a. 40
b. 25
c. 12.5
d. 5

Student Responses:

No data yet. The correct response is c.

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