A sample of moon rock was brought back from the latest moon mission. Scientists are eager to date this rock to see when it was formed. They will use a technique called radiometric dating. Their data is shown below. Help the scientists calculate and draw conclusions about each sample.
Potassium-40 decays into Argon-40, known as K-Ar dating. Potassium-40 has a half-life of 1.25 billion years.

Identify the number of half-lives passed after 2.5 billion years.
Explain how you came to this conclusion.