DD's advice is to "think out loud". When they pose a question, don't just rattle off the answer, or make something up on the spot, but go through all the steps you need to come up with the answer. She said it didn't seem to matter that she didn't know certain things (the caloric value of a bar of chocolate - why would she? She is a size 6 and still fits in age 12-13 clothes at 23...!) so they guided her to guess. She was put in the "worth a place" category and snapped up by her present college. The Head of Admissions at her college told us that she was his best pick from the pool of 2016. It's almost certainly an exaggeration to proud parents at graduation, but she has done really well there.
Good luck to all the DC. The best parental advice I can give is to leave them to it. If they are successful and then make the grades, you won't be able to micromanage them, so for now offer good food, plenty of warm drinks and hugs. Then hit the gin yourself!