Posted on
23
Apr 2021

## Standard Deviation – Clustering (Birds) Problem

Hey guys! Today we’re going to take a look at a DS problem that is a skills problem, focused on GMAT standard deviation.

#### Standard Deviation & Variance

What they’re asking here is do we have enough information to compute a standard deviation? It’s useful to think of standard deviation as clustering. If we have a whole series of points we can define how clustered or un-clustered the group of points is. That’s all that’s standard deviation, that’s all that variance is. So if we have all the points that works. What we should be on the lookout here for are parametric measurements. Especially things like the average number is, because while the average can be used to compute standard deviation, we need to know how each of the points differs from the average. But if we have each of the points we always get the average. That is, we can compute the average. So the average is a nice looking piece of information that actually has little to no value here. So let’s jump into the introduced information.

#### Statement 1

Number 1 BOOM – tells us that the average number of eggs is 4 and that’s great except that it doesn’t tell us about the clustering. If we run some scenarios here we could have every nest have 4 eggs or we could have 5 nests have 0, 5 nests have 8, or 9 nests have 0, 1 nest has 40. These are all different clusterings and we could end up with anything in between those extremes as well. So number 1 is insufficient.

#### Statement 2

Number 2: tells us that each of the 10 bird’s nests has exactly 4 eggs. What does this mean? We have all 10 points. They happen to all be on the average, which means the standard deviation is 0. that is there’s no clustering whatsoever. But 2 gives us all the information we need so B – 2 alone is sufficient is the answer here.

Hope this was useful guys, check out the links below for a video about how to compute standard deviation as a refresher, as well as other problems related to this one. Thanks for watching we’ll see you again real soon

If you enjoyed this GMAT problem, try another one next: Normative Distribution

Posted on
31
Mar 2021

## Ace GMAT Data Sufficiency Questions with this Science Fair Problem

### Data Sufficiency Problem Video Transcript

#### Introduction to Data Sufficiency

Hey guys! Today we’re looking at the Science Fair Problem. In this Data Sufficiency, we’re being asked how many, discrete number, of the 900 students at the school attended all three days. And we can surmise that they’re going to come at us by giving us different breakdowns of how different groups of students behaved and so most likely we’re going to need more than one piece of information to come together in order to give us the precise amount. The only way, typically, that we would have a single piece of information be sufficient is if they gave us the inverse and told us how many, or what percentage, or what fraction of students didn’t attend on all three days. Where we could then compute the opposite.

#### Statement 1

Let’s take a look: Number 1 is telling us that 30% or 270 of the students attended two or more days. If we break this up into a chart, we see this block that’s undefined but we know that 270 attended either two days or three days. Some mix of them, but we don’t know that mix. Therefore, this doesn’t give us what we need from the box and it’s insufficient. However, we could use it possibly with other information that distinguishes between the two day visitors and the three day visitors.

#### Statement 2

Number 2 gives us relative information based upon some other number: 10% of those that attended at least one day. That means of all those that attended at all, for one day, for two days, for three days, 10% of those belong in the three-day box. However, we don’t know how many students that is. So 2 is insufficient. When we try and combine them notice that the information from 2 slices and dices a piece of information that 1 doesn’t give us. There’s no way to reconcile the 10% from that big group into the group that just attended two days or three days. Therefore, we don’t have enough information.

The answer choice is E: both together are still insufficient. Hope this helped. Guys thanks for watching! For other examples of DS problems where you can make charts to fill in the blanks and find the square you need check out the links below and we’ll see you again soon.

If you enjoyed this Data Sufficiency problem video try this Standard Deviation Problem