The scoring of the official practice tests is basically the same as that of the real GMAT. So, if you perform at the same level on the real GMAT, you can expect to get the same score.
It's amazing that you can miss 10 questions on a practice test and score Q50, but because the GMAT considers the difficulty of the questions you miss and get correct, as long as you get all the easy and medium questions you see correct and miss only the hardest questions, you can miss quite a few and score high on quant.
That said, on the real GMAT, only 28 of the quant questions count - the rest of the questions are experimental questions - and you can't miss 10 counted quant questions and score Q50.
To get a clearer sense of how many questions you need to get correct to achieve various GMAT quant, verbal, and total scores, see this post.
How Many Questions Can I Get Wrong on the GMAT and Get 700?