Why CodeChef deduct rating?

Whenever I participlate in a contest. Codechef deducts my rating. Why?

rating not only depends on solving the problem but also depends on how fast you have solved it.
if you participated in a contest and failed to solve any problem you will lose points (like i lose 200 points in one competition).

You should ask this question to toursit that why whenvever he participates in a contest codechef increases his ratings :wink: :wink: :wink: