What is the purpose of including unnecessary(?) arguments in this function?

You're right. Based on what you're telling us, there doesn't seem to be any reason to have 3 arguments in there.

Maybe the question wanted an answer like this?

// allows you to pass in a custom return value for true/false cases
function isEven(a, b, c) {
    if (a % 2 === 0) {
        return b;
    }
    else {
        return c;
    }
}

var extraCredit = isEven(5, "even", "odd");

I can't imagine why anyone would want to go to that degree of effort for something so simple though.

Maybe there's something else going on in the context of the question that we're missing. I don't know what question you're referring to though so it's hard for me to say...

I wonder this extra credit problem comes from which Treehouse course.

Thanks, Jessica. I guess there really is no right answer. I remember the person who suggested Treehouse to me basically saying there are no right answers, just more efficient ways of doing things. This is that, I think. Glad I asked. Your answer got me thinking outside of the box.

William: I should have included that. Thanks. http://teamtreehouse.com/library/introduction-to-programming

People have apparently been wondering about this for a long time: https://teamtreehouse.com/forum/extra-credit-for-functions-badge

Someone people theorize that you're supposed to check if the sum of a, b and c is even or odd. I'm so curious now, I hope someone answers.