question about plugging in numbers

[wawatan]

if in the question, it has variable x and y

could you put the same number for x and y?

for example can we say x=4 y=4 ....any suggestions? i'm having trouble plugging number for data sufficiency problems with number properties....


:

[VP_Jim]

In problem solving, it's generally a bad idea to use the same number for multiple variables. Also, it's generally a bad idea to use 0 or 1, or any number that appears in the answer choices. This is because 0 and 1 have different properties than other numbers, and funny things can happen when they are used (and, when you use the same number for both variables and end up dividing x by y, you end up with 1).

Data sufficiency is the opposite: you *want* to use the numbers with the funny properties. So, go ahead and use 0 or 1, or the same numbers, or extreme numbers, or positives and negatives and fractions. Go nuts!

Hope this helps!

[lunarpower]

if in the question, it has variable x and y

could you put the same number for x and y?

for example can we say x=4 y=4 ....any suggestions? i'm having trouble plugging number for data sufficiency problems with number properties....

:

if you're doing a data sufficiency problem, the issue is to recognize the TYPES OF NUMBERS that are ASSOCIATED with each operation that you're going to deal with.

for instance:
if you see ABSOLUTE VALUE in a data sufficiency problem, then you should know right away that the problem will revolve around whether the numbers in the problem are POSITIVE, NEGATIVE, or ZERO.

if you see COMPARISONS BETWEEN POWERS of the same variable - for instance, x^2 < x - in a data sufficiency problem, then you should know that positive/negative/zero matters, but also that GREATER / LESS THAN 1 (and also -1) matters as well. this is the case because powers of 'normal' numbers (like 2 and 3) are bigger than the numbers themselves, but powers of fractions (between 0 and 1) are smaller than the original numbers.

etc.

once you get the gist of it, you'll have an idea what sort of numbers to plug in.

--

as the post above says, you might want to shy away from picking the same # for two or more variables ON PROBLEM SOLVING PROBLEMS. however, if you're solving a data sufficiency problem, you may well want to plug in the same number for the two different variables just to see what happens; on certain number properties problems, that may be the exception that disproves the rule. for instance, here's a relatively simple problem that i just made up:
is (x - y)^2 positive?
(1) blah blah
(2) blah blah blah

in this case, the only way (x - y)^2 can't be positive is if x = y, so, if you avoid plugging in equal numbers wholesale, you might wrongly conclude that a statement is sufficient when it actually isn't.