ACT Science Practice Question #1482 (Medium (32)) | Test Citadel
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ACT Science Difficulty: Medium (32)

Digital ACT Science Practice Question #1482

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Geologists analyzed the ratio of parent isotope potassium-40 (K-40) to daughter argon-40 (Ar-40) in volcanic ash layers within a sedimentary basin. The half-life of K-40 is 1.25 billion years: - Layer A: 12.5% K-40 remaining, 87.5% Ar-40 - Layer B: 25.0% K-40 remaining, 75.0% Ar-40 - Layer C: 50.0% K-40 remaining, 50.0% Ar-40 What is the estimated absolute age of volcanic ash Layer B?
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25% remaining = 2 half-lives. 2 * 1.25 = 2.50 billion years.

Masterclass Solution & Distractor Trap Analysis

25% remaining corresponds to 2 half-lives (100% -> 50% -> 25%). 2 * 1.25 billion years = 2.50 billion years....

Distractor Analysis: Trap choice eliminates careless test-takers who confuse roots with coordinates...

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