Final answer:
The fraction of a given amount of hydrogen-3 that would be left after 36.9 years of decay is approximately 0.125 or 12.5%.
Step-by-step explanation:
Tritium (hydrogen-3) has a half-life of 12.3 years. This means that after 12.3 years, half of the tritium will have decayed. After another 12.3 years, another half of the remaining tritium will have decayed, and so on. So, if we start with a given amount of tritium, the fraction that would be left after 36.9 years of decay can be calculated using the formula:
Fraction left = (1/2)^(36.9/12.3)
Therefore, the fraction of the given amount of tritium that would be left after 36.9 years of decay is approximately 0.125, which is equivalent to 12.5%