I'm actually taking my DAT in about 6 days, but what I've been doing to study and what you should you...
If you have a weak background in QR, I'd suggest you go through the math section in Kaplan's BB. It is extremely basic, but you should really need to know the basics. If that doesn't seem sufficient, I suggest you get a SAT study book and just skim through the math section. Under NO circumstances should you rely on those alone. I haven't heard of Khan, and for Chad I'd only use him for GC and OC
The real heart of the QR is how fast can you work through it without making stupid mistakes haha. This really comes with just oodles of practice practice practice! It's not really something you learn and memorize. It's just something you do a lot of and learn to recognize what you need to do quickly.
Destroyer sciences + math has about 150 questions for math.
Destroyer math has 12 practice tests
Both of them are excellent for practice and you should go through all of them with the time limit. Then go through all the solutions, make sure you know how to do them, and go through them again the next day with a time limit. The two books kind of test two separate groups of math concepts, but if you're strapped for cash/time, I'd go with Destroyer math only. With that book, do NOT worry about tests 11/12 as they jack up the difficulty/wordiness level and your real DAT math supposedly only will have like 1 or 2 kinds of questions that the entire test 11/12 are made of. Even I (a math loving Asian) had problems finishing more than 30 in the given time. BUT you should still go through them (no matter how painful) so that you know what to do with questions like those.