Well, I wouldn't spend too much time with this test, but to answer your questions:forgetneoiamtheone wrote:Q5: yes, Pi is needed for this question.Ian Stewart wrote:Thanks for the info. Yeah, for a few of those questions, they've just changed a detail or two in questions that are freely available in GMATPrep. I just completed that test, and in case anyone else bothers with it, I'd point out that there are at least four fundamental mathematical errors in their twenty questions (question 5 needs Pi in the correct answer choice, 6 can't possibly be answered with the information given, 10 doesn't have the right answer among the choices and 18 needs to specify that m and n are integers), so proceed with caution.wizardofwashington wrote:I ended up finding this in my RSS feed, but then went searching for the real source, which is this Test Prep company's (MLIC, aka ETS) sample test. This question along with a few other tough ones are offered as "samples" for those visiting their website:pre-gmat wrote:Yes, I was surprised too.
The original GPrep question is h(100)+1.
But never saw repeat of this question anywhere.
WizardofWashington, where did you get this from?
https://www.mlicets.org/gmat/gmat-practice-test.html
Q6: I choose (6,6), the choice that changes the mean least. SD is a function of "spread of samples from mean". Numerator captures the absolute spread and the denominator normalises it. Denominator would be same for every choice, so what matters is what choice gives you the least "numerator", and it should be the choice that changes it by least amount(in this case 6,6 wouldn't change mean at all). In all other choices, mean will change and atleast one of the added numbers will be "far" from the resulting mean. Agreed, this is not very mathematically rigorous approach, and just an intuitive one.
Q10: I got 9/55 with a crucial assumption.
From the info, number of blue balls compute to 3.
So third blue ball: (6/11)*(3/10), of course the assumption here is that third ball is being drawn after probablistically drawing first two red balls.
The answer would be simply 3/10, if the first event of drawing two red balls is given to have occured.
Q 12? What is the cleanest and fastest way to the answer for this one?
And what is the part played by this piece of info: "equally space points"
Thanks
Q6- if the standard deviation is very large, then adding the elements (6,6) will lower the standard deviation more than adding elements (0,12), for example. It's simply impossible to answer the question from the information given. Incidentally, this question is based on a GMATPrep question (it's almost identical) which asked 'which pair of values, if added to the set, will lower the standard deviation the most'. But when they changed the question, they made it into mathematical nonsense.
Q10- it's unclear what the question means. If they mean 'if, after picking two red balls, what's the probability the third is blue', the answer is 3/10. If they mean: 'given this situation, what's the probability the third ball drawn is blue if you pick three balls', then the answer is 1/4. Either of those interpretations is suggested by the wording of the question. But, judging by the 'correct answer', what they actually mean is- 'what's the probability of picking a red ball, then a red ball, then a blue ball', to which the answer is indeed 9/55. But that's not what they ask.
Q12- it's irrelevant that the points are equally spaced. To make a triangle, you need to choose two points from one line (where order is not important) and one point from the other line. Of course, we could choose the pair of points from the first line, the single point from the second, or we could choose the pair of points from the second line, and the single point from the first. So the answer will be (6C2)*5 + (5C2)*6.
