High School

Potassium-40 has a half-life of \( 1.27 \times 10^{9} \) years. You have a modern sample that now has \( 97.3 \% \) of the amount you expected your sample had at the start. How old is your sample?

Answer :

Potassium- 40 has a half-life of 1.27 x 10⁹ years. You have a modern sample that now has 97.3% of the amount you expected your sample had at the start. The age of the sample is 3.43 billion years old.

The half-life of potassium-40 is 1.27 x 10⁹ years. This means that half of the potassium-40 atoms in a sample will decay after 1.27 x 10⁹ years.

Calculate the percentage of potassium-40 atoms that have decayed:

percentage decayed = 1 - 97.3 = 2.7

If your sample now has 97.3% of the amount of potassium-40 that it had at the start, then this means that 2.7% of the potassium-40 atoms have decayed.

Calculate the number of half-lives that have passed:

number of half lives = percentage decayed / 0.5 = 2.7 / 0.5 = 5.4

Calculate the age of the sample:

age = number of half lives * half-life = 5.4 * 1.27 x 10⁹ = 3.43 x 10⁸ years

Since half of the potassium-40 atoms will decay after 1.27 x 10⁹ years, then 2.7% of the potassium-40 atoms will decay after 3.43 x 10⁸ years.

Therefore, the age of the sample is 3.43 billion years old.

To know more about half-life here

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The complete question is:

Potassium- 40 has a half-life of 1.27 x 10⁹ years. You have a modern sample that now has 97.3% of the amount you expected your sample had at the start. How old is your sample?