The measurement of radioactive decay can be useful tool in things such as carbon-dating. for a carbon sample with mass 500kg and a half life of 5,730 years, calculate the remaining mass after 20,000years.

The first one, i believe, would be correct. all the others have one thing in common, and that's that they have repeating numbers. in the second one, x and y have repeating 6's and 3's, and in the third, x and y have repeating 6's as well. in the last one, there are repeating 3's. the first one has no repeating numbers.

(answer 2 )i’m very smart that’s how i know the answer.