Relative/Concrete Value and Overlapping Sets

[Twan N]

Hi,

I have a couple of questions for the above two subjects. First, regarding relative and concrete values, the MGMAT FDPs guide provided a shortcut for them on DS questions as followed:

"If a DS question asks for the relative value of two elements of a ratio, any statement that provides any two elements of a ratio is sufficient.

If a DS question asks for the concrete value of an element of a ratio, then you'll need the concrete value of another element of a ratio AND the relative value of two elements of a ratio to be sufficient"

My question is this, the above shortcuts apply only to ratios of two quantities correct? such as a:b:total, and not to ratios of three or more quantities such as a:b:c:total because even when you are given 2 elements, the third element (say c for example) is still unknown. This wasn't specify in the guide so I want to make sure I have a clear understanding.

The second question I have is about overlapping sets. The two formulas I came across with overlapping sets are:

Total = Group 1 + Group 2 - Both + Neither (I understood how to derive these from the double-set matrix)

Group 1 or 2 = Group 1 + Group 2 - Both

Now, how do these two equations related, it seems to me the Group 1 or 2 value in the second equation is equal to the Total - Neither from the first equation. Am I correct?

Thank you for any input.

[RonPurewal]

It's important that you not try to memorize meaningless rules for this kind of stuff. You can use statements like these an a guideline, but the ultimate goal is to be able to form an intuition about this material.

Hi,

I have a couple of questions for the above two subjects. First, regarding relative and concrete values, the MGMAT FDPs guide provided a shortcut for them on DS questions as followed:

"If a DS question asks for the relative value of two elements of a ratio, any statement that provides any two elements of a ratio is sufficient.

If a DS question asks for the concrete value of an element of a ratio, then you'll need the concrete value of another element of a ratio AND the relative value of two elements of a ratio to be sufficient"

My question is this, the above shortcuts apply only to ratios of two quantities correct? such as a:b:total, and not to ratios of three or more quantities such as a:b:c:total because even when you are given 2 elements, the third element (say c for example) is still unknown. This wasn't specify in the guide so I want to make sure I have a clear understanding.

I don't know exactly what is meant by "relative value" here. Maybe that means the coefficients of the ratio (in which case you'd be better off just saying "coefficients of the ratio"). I don't know.

In any case -- no, even if you have a ratio of lots and lots and lots of things, one concrete ratio is enough to fix all of the other values in the ratio.
For instance, let's say I buy seven items at the grocery store, with prices in the ratio 1:2:3:4:5:6:7.
In this case, if I'm told that the fourth item costs, say, $16, then I have all seven prices ($4, $8, $12, $16, $20, $24, $28).

[RonPurewal]

The second question I have is about overlapping sets. The two formulas I came across with overlapping sets are:

Total = Group 1 + Group 2 - Both + Neither (I understood how to derive these from the double-set matrix)

Group 1 or 2 = Group 1 + Group 2 - Both

Now, how do these two equations related, it seems to me the Group 1 or 2 value in the second equation is equal to the Total - Neither from the first equation. Am I correct?

Thank you for any input.

They're the same, but the second carries the assumption that no one/nothing is in the "Neither" group.
You may as well just stick with the first one, since that covers all possible cases anyway.

(If you make the Double Set Matrix as detailed in our strategy guide, then there's no need to worry about these formulas in the first place -- the chart will take care of the math automatically!)

[RonPurewal]

By the way -- From now on, if you have more than one question and the questions deal with unrelated topics, please post different threads for different topics.

If you have further questions about either of these items, please start a new thread about one issue. If you have further questions about both of them, please start two new threads.

Thanks.