Question

In a multiple-choice test, each question has five options. Students will get 10 points for each correct answer; lose 2 point for each incorrect answer; and receive no points for unanswered questions. A student does not know the correct answer for one question. Is it to her advantage or disadvantage to guess an answer? Show your calculations for expected value. Show your work for full credit.

Answer 1

Chance to get it right: 1/5
Chance to get it wrong: 4/5
Points if right: 10
Points if wrong: -2
Unanswered: 0

Now I have an idea on how to do it although I'm not sure. It's been awhile.

Answer 2

But your not sure it right?

Answer 3

No, I'm not :/