Question

If the half-life of K-40 is 1.3 billion years and if a sample rock found on an island is estimated to be 1 billion years old, what percentage of the original parent K-40 would be present in the rock? Round your numerical values to the hundredths decimal place.

Answer Choices

(A) 76.92%
(B) 1.3%
(C) 58.67%
(D) 99.99%

Answer 1

For this case, we must make a rule of three, to find the percentage of the k-40 found in the sample found.

1.3 ----------> 100%

1 -------------> x

Where "x" represents the percentage of k-40 present in the sample found.

`x = \frac {1 * 100} {1.3}\\x = 76.9230`

Rounding off we have:

76.92%

ANswer:

Option A