Insurance Calculation

[prohornblower]

If I wanted to offer a friend insurance for a $102 test in which I estimate he has only about a 40% chance of passing, how do I calculate the rate?

Say I want to add a flat $10 fee for profit. I've come up with a couple numbers, one was like $73, and the other $19...so there is a large disparity in my calcs.

Thanks!