13)
The half-life of carbon-14 is 5730 years. Explain how to figure out the age of a substance that has 25% carbon-14 remaining.
A) Multiply 25% times 5730 years since only 25% of the carbon remains.
B) Divide 5730 years by 2 since carbon has gone through two half-lives.
C) Multiply 5730 years by 2 since two half-lives have gone by for carbon.
Eliminate
D) Multiply 4 times 5730 years since carbon has gone through 4 half-lives.

Multiply 5730 years by 2 since two half-lives have gone by for carbon.

Explanation:

The half-life of a radioactive isotope depicts the measure of time that it takes half of the isotope in an example decay. On account of radiocarbon dating, the half-existence of carbon 14 is 5,730 years  

The half-life of carbon-14 is 5730 years.  

In this manner, after  

1 half-life there is 50 % = 1/2 of the first amount left.  

2 half-lives there is 25 % = 1/4 of the first amount left.  

25% is two half-lives.  

Every 50% of life requires 5730 years.  

So two half-lives require 2 × 5730

on island x the species needed to adapt because they were being subject to predators which didn't inhabit island y.