I went through two rounds of the five it takes to secure a summer intern spot. The first one is an in person interview where they ask you to do mental math. They generally don't ask any finance questions. The second round was brainteasers and harder logic math. The people were really nice, but in the end, acceptance is based on the skill you bring. Don't be afraid to answer a question wrong at first, as long as you don't panic, and correct yourself.