Answer:
1845 years
Step-by-step explanation:
Decay of Carbon-14 is usually modeled by an exponential function. It x is the number of years since the original amount was brought into existence, then the fraction remaining (y) is modeled by ...
... y = (1/2)^(x/5730)
We want to find the value of x when y = 80% = 0.80. The equation is then ...
... 0.80 = 0.50^(x/5730)
Taking logarithms, we get
... log(0.80) = (x/5730)·log(0.50)
Multiplying by the inverse of the coefficient of x, we have
... x = 5730·log(0.80)/log(0.50) ≈ 1845 . . . . years
