You have an isotope with a half-life of 200 years How much of the original material is left after 600 years?

of its original size would be left

Explanation:

The half life of the isotope is the time required for it to decay to half of its original size.

Half life of the isotope = 200 years

So that, after 600 years the material that would be left would be;

let the original size of the material be represented by x.

200 years = x would remain

400 years = x would remain

600 years = x would remain

Thus after 600 years, of its original size would be left.