Data Sufficiency

lunarpower wrote: in any case, it's clear that the intention of the problem is to get the student to realize that the negative solution is not ok (since the "√" sign always refers to the positive square root of a number). if this is our problem, i'll think of a less tricky way to phrase the problem so that this purpose is preserved.

gmatrant wrote:Is there a difference between raising the expression as: X^1/2 and sqrt(x).
I am assuming that both are same. So why would the original post be wrong if it read x^1/2 and not sqrt(x)

selango wrote:Each number has 2 square roots. However, the notation sqrt(x) represents the principal square root which is always positive. To represent the other (negative) square root, the notation is -sqrt(x).

Is the above statement correct?

This means sqrt(4)=2 and -sqrt(4)=-2

lunarpower wrote:i looked in our database. this question is ours, but it's currently deactivated -- i.e., it's not active in the CAT pool, so you shouldn't have seen it while you were taking the exam.

the only thing i can't see is the date on which the problem was deactivated. this thread is dated last week, which is a bit surprising -- i don't think that we've actually deactivated any questions in the last week -- but i can check with other members of the CAT problem committee.

in any case, i'll just reiterate the two things that i already said:
(1) the wording in this problem is still totally legitimate, from a mathematical standpoint. the "product of all numbers in a set" is perfectly well defined when the set contains only 1 number; the "product" is just that number.
HOWEVER,
(2) this problem is problematic, in that it's not representative of what has historically appeared on the exam. to date, i haven't seen a wording as "tricky" as this one.

--

incidentally, the parentheses in the word "solution(s)" are a VERY strong hint that you shouldn't neglect the possibility of having only a single solution.

lunarpower wrote:

sanju09 wrote: Totally agree Ron, but what about the ordering of choices, was that really not taken care of, originally?

three things --
1) the answer choices shown in the current database are -4, -2, 0, 4, 6. so i don't know where this poster got these answer choices.
in fact, you posted this question here, with the correct answer choices:
https://www.beatthegmat.com/possible-sol ... 34823.html

... so i have no idea where this person got these answer choices. they aren't in our database, so they must have gotten the whole question from a second- or thirdhand source.

2) it's not actually true that the answer choices are always in order on official problems; see, e.g., problem solving #54, 70, and 138 in OG12.
however, it's true that i've never seen a problem on which a list of five whole numbers is out of order.

interestingly, in ratio problems in which the answers themselves are ratios, i've noticed that the five ratios (if treated as fractions) are out of order in almost all of the problems.

3) this is far less of a big deal than it would be in problems involving fractions, roots, etc., since the order of five integers is obvious even if they are not listed in order.

Stuart Kovinsky wrote:

dinesh19aug wrote:Selango,
I am sorry but your answer is incorrect. The OA is +4.

The explanation says: When you square the two sides you introduce an ambiguous root. It MAY OR MAY NOT satisfy the equation. Try putting it "-1" in the original equation and you will see that you get

-1 = (-3 + 4)^1/2
which gives you -1 =1

Hence the only valid root is 4, which is the OA.

Did you copy the question exactly? Or did you add the "^1/2" because you couldn't copy the square root sign properly?

If the right side were "sqrt(3y + 4)", then it would only include the positive root. However, if it's reproduced correctly, then it should include both the positive and negative root.

kvcpk wrote:I think I found the right thread to post my question.

As per what I have heard, on the GMAT Land,
If it is given,
x = sqrt(36), then x=6
if it is given
x^2 = 36, then x can be 6 or -6

Am I right?

Then what about sqrt(x^2) ?