Timing on 3 Overlapping Sets Problems

[ericheidt1123]

Hello MGMAT,

Overlapping set problems with three venn diagrams kill me on time. The difficulty level noted in Navigator tends to always be "Devilish" but I assume this is because of the time and not problem difficulty.

I am consistent with getting the correct answer, but creating a venn diagram and assigning the spaces (a+b+c+g... etc..) is a significant amount of work. Even after I go BACK to the problem immediately and attempt again with the known strategy, I just can't push the work out any faster than about 4 minutes. I rarely struggle on time with other quant problems. This is my slowest question type.

Any tips?

Thanks,
Eric

[RonPurewal]

It's hard to opine on this issue without seeing specific examples. If you post a particular problem(s)--in the appropriate folder, depending on the source--and narrate some of the difficulties you're having with it, that would help.

The only super-general piece of advice I can dispense is that you should try to group the quantities when possible.
It seems that you're using a separate letter for every little bitty region in the diagram; that may not be necessary. For instance, you may be able to handle all of the "two out of three, but not the third" regions at once. Or all of the "only one of the three" regions at once. And so on.

[RonPurewal]

There's also a formula:
(Number in set A + number in set B + number in set C) minus (number in sets A,B + number in sets A,C + number in sets A,C) plus (number in all three sets) = total number of items.

This formula is terribly intimidating (to me, anyway) at first, but there's a certain elegant symmetry to it. If necessary, you can derive it by thinking about "double-counting" or "triple-counting"--that's what I have to do, as I'm not really capable of remembering such things cold--but that, of course, would take some additional time.

[ralphh539]

Any other tricks to learn sets? thoroughly?

[tim]

"Sets" is not something tested at more than the most rudimentary level on the GMAT in my experience. If you're talking about overlapping sets, we have a chapter devoted to covering that topic in detail in our Word Problems strategy guide.