When you take the dat, just go through all the ones you can do. Skip/mark random bubble in the ones you can't get quickly. Go back afterwards and do the ones you may solve but takes time 1-2 min. If its a question requiring 2+ min just mark and skip it. It's hopeless on those ones.
You can miss I think 10-12ish??? and get a 17-18. So go by that standard. I got an 18 on my QR and did just that- and I'm TERRIBLE at math.