parulmahajan89 wrote:
Does plug in number works here? for Statement 2?
Plugging numbers typically works best when you suspect that the statement is not sufficient. In these cases, all you need to do is find values that yield different (conflicting) answers to the target question.
If it turns out that the statement is sufficient, then plugging in values will only give you a general idea of whether or not the statement is sufficient, but you won't be able to make any definitive conclusions.
For example, let's say we have the following target question:
Is x > 0?
Let's say statement 1 says: 5x > 4x
Now let's plug in some values of x that satisfy the condition that 5x > 4x.
x = 3, in which case
x > 0
x = 0.5, in which case
x > 0
x = 15, in which case
x > 0
x = 1000, in which case
x > 0
So, it APPEARS that statement 1 provides sufficient information to answer the target question. But can we be 100% certain? No. Perhaps we didn't plug in the right numbers. Perhaps there's a number that we could have plugged in such that
x < 0
If we want to be 100% certain that a statement is SUFFICIENT, we'll need to use a technique other than plugging in.
Here, we can take 5x > 4x, and subtract 4x from both sides to get x > 0 VOILA - we can now answer the target question with absolute certainty.
So, statement is SUFFICIENT.
To illustrate the potential problems with plugging in, consider this target question:
Is positive integer k a prime number?
Statement 1: k is an odd integer.
We should recognize that statement 1 is not sufficient, but notice what happens if we don't choose good numbers to plug in. If x is odd, then here are some possible cases:
x = 3, in which case
x is prime
x = 5, in which case
x is prime
x = 7, in which case
x is prime
Well, I've already plugged in 3 odd integers, and they all led to the same conclusion. So, x must be prime, right? Of course, this is the wrong conclusion.
So, be careful when plugging in values. The only time this technique yields
definitive conclusions is when the statement is not sufficient AND you're able to find plug-in values that yield different answers to the target question.
For more information about this important concept, you can watch our free video:
https://www.gmatprepnow.com/module/gmat- ... cy?id=1101
Cheers,
Brent
