I have had several students score a Q51 even while using 4 "skips" on the math section - so you don't still have to answer absolutely everything. Obviously, you have to be very, very good to get a Q51.
If you go into the test with the mindset that you do have to try to get everything, you risk blowing lots of time and mental energy on 1-2 problems and then missing other, lower-level problems because you are rushing and/or making careless mistakes. That's what will prevent you from hitting Q51 (assuming in the first place that one is capable of performing at that level - obviously
So this mindset still applies. You can't bail on 6-7 plus get a lot of others wrong. But you can still bail on some and get some others wrong.
I'll also point out: if you don't know how to do the problem sitting in front of you right now, the only good thing you can do is acknowledge that and move on. You can't will yourself to get it right just because you know you can't afford to get many wrong and still hit 51. And one more thing: GMATPrep is a little less forgiving. The real test has somewhere between 5 and 10 experimentals (best guess: probably 6 or 7). You can get every single one of those wrong and that won't impact your score in the slightest! Plus you can miss some that count and still get a 51.
The real trick to hard smart numbers (or VICs) problems is figuring out what kind of a number will be a good number to test and figuring out where to start if there are multiple potential starting points (ie, I could pick for x or for y or for z). I would go through the OG, GMATPrep, and whatever other official resources you have, looking for all of the problems that could be solving via smart numbers (and testing cases and working backwards and estimating...). Try them. Then think about how the math worked and what numbers would be better / make the math easier and try that. As you go, keep asking yourself why. Oh, I see, I get 0.5 here, but it I'd started with an even number, I'd get an integer. Okay, is there a clue I could've spotted sooner that should've lead me to choose an even?
Or how about this:
Kim makes 80% of what Ami makes and Ami makes 110% of what Rahul makes. What's the ratio of what Kim makes to what Rahul makes?
Kim is first in that sentence, so let's say K = $100. Now, $100 is 80% of what Ami makes... that's annoying. I'd rather know that Ami makes $100 and then just take 80% of that to find Kim.
Okay, forget K = 100. Let's say A = 100 and K = 80. Now, Rahul...oh. I see. That's annoying again because Ami takes the same "position" that Kim takes in the next part.
So I really want to start with Rahul. If Rahul = 100, then Ami = 110, and Kim = 0.8(110) = 88. Ratio of K:R = 88:100 = 22:25.
Now, how am I going to know next time I see something similar, so that I don't have to waste time figuring out that I should start with Rahul?
Look at the text of the problem: Kim makes 80% of what Ami makes and Ami makes 110% of what Rahul makes.
The first part would translate algebraically to K = 0.8A. So it's easier to pick for A and then take 80% to find K. Similarly, A = 1.1R. Ditto easier to plug in for R. So in the future, I want to remember two things: pick an x% OF person to start (because of signals that multiplication). And, ideally, pick someone who shows up ONLY in that x% OF position. In the above problem. Ami shows up in the x% of position once, but the second time, she's on the other side of the equation. Only Rahul is all by himself on the OF side.
That kind of thing. Practice. And then think about what happened and why and try it again...and again...and again, tweaking until you find the optimal approach and know how to recognize when to use that approach in future. If you're going to hit a 51, you've got to be able to do this.
We have tons of articles on these strategies on our blog - literally just search for Smart Numbers, Test Cases, Work Backwards, and estimate. And here are some other ones to make you think:
https://www.manhattanprep.com/gmat/blog ... them-real/https://www.manhattanprep.com/gmat/blog ... ms-part-1/https://www.manhattangmat.com/blog/2013 ... 0-seconds/https://www.manhattanprep.com/gmat/blog ... m-solving/Good luck!