Dinosaur fossils are often dated by using an element other than carbon, like potassium-40, that has a longer half life (in this case, approximately 1.25 billion years). suppose the minimum detectable amount is 0.1% and a dinosaur is dated with 40k to be 67 million years old. is this possible?

The equation relating radioactive decay is:

N(i) = N(o) * exp(-0.693*t / t(half))

The fraction:
N(i)/N(o) represents the fraction of original substance present after t years and a half-life of t(half). Substituting the values,

N(i)/N(o) = exp((-0.693 * 67)/(1,250))

N(i)/N(o) = 0.964 or 96.4%

This means that the amount is far above the minimum detectable amount, so this method is feasible.