One of the great benefits of the Veritas Prep Question Bank is that with its 4 million user responses to GMAT practice questions it does an excellent job of highlighting test-taker trends. These statistics can point out trap answers that examinees too readily fall for, conceptual areas that students need to address, and other valuable insights into the way the world takes the GMAT. And this week, one particular trend caught our eye in a major way:
Test-takers struggle mightily with the concept of “Rate of Change” vs. “Actual Number”.
Consider this quick data table, which displays the average monthly temperature in Chicago, Illinois:
Month…….Average High Temperature
Now, from a quick glance you should see that the temperature increases every month from February through July. But there’s another angle to this data, too, and challenging Integrated Reasoning questions can hinge on that exact point. The temperature INCREASES every month, but the GROWTH RATE declines – from February to March the temperature increases by 11.4 degrees, but from June to July it only goes up 4.3 degrees as summer temperatures level off. So while the data table above might clearly demonstrate that the temperature is rising (we promise, Chicago – although we know it hasn’t been too noticeable just yet!), an Integrated Reasoning question might show you this graph:
Based on this graph, most students would incorrectly answer the question: “From March through August, how many months did the average temperature decrease?”, as most would look at the graph and see several months of decline. But the important thing to keep in mind is “WHAT declined?”. And in this case it’s “the growth rate in the temperature” not “the temperature itself”. In this graph, any time the data point is above 0, that means the temperature increased. Only one month (August) was colder than the month prior.
This next graph will plot both “average temperature” and temperature growth” together to highlight this concept.
So what is the lesson? Make sure that you’re aware of the difference between the “actual number” and the “rate of change” and that you look for that concept to be tested on Graphics Interpretation questions. When newscasters say that “Apple’s earnings growth dropped 5% this quarter” that doesn’t necessarily mean that Apple lost money or didn’t improve upon the last quarter; it just means that it grew slower. Think back to physics classes and the difference between acceleration and velocity – “percent change” is the acceleration component, but people often mistake it for the velocity. And based on Question Bank data, every time this concept has been tested more than half of users missed this concept!
So remember – the rate of change can decline while the actual number still increases…just not as quickly. Understanding and recognizing this concept can keep both metrics positive for your Integrated Reasoning score.
By Brian Galvin