A2,000 g quantity of c-14 is left to undergo radioactive decay. the half-life of c-14 is approximately 5,700 years. after going trough x half-lives, the sample becomes 125 grams. what is x?

Start with 2,000 grams.
After 1 half-life, 1,000 grams are left.
After another half-life, 500 are left.
After another half-life, 250 are left.
After another half-life, 125 are left.

That was FOUR half-lifes.

X = 4 .