Have you watched Chad's videos? I highly recommend them. He goes over things that you probably haven't seen since high school and gives you shortcuts for different types of problems that saves a ton of time.
I think I know which standard deviation problem you're talking about. For those problems, knowing the standard deviation formula isn't necessary. Just look to see which of the choices has the largest range. If the ranges are the same, find the one that has the most variance. For example, take a look at these sets:
A. [2 4 6 8 10]
B. [15 17 19 21 23]
C. [6 8 8 12 14]
All 3 sets have the same range, so that doesn't tell us which std dev is greatest. You can see that A and B have the same variance, whereas C has a higher variance and therefore a greater standard deviation.