Question

Write 6.816 correct to one decimal place

Answer 1

6.8 because you only need one decimal place, you can leave the other two given decimal places out.

Answer 2

We don't know what's correct, because we don't know anything about
where the number came from. If you want the number ROUNDED to
one place, that's  6.8 . If you want it TRUNCATED (shortened, trimmed)
to one place, that's also  6.8 . But we have no idea whether either digit is correct.