DI Step Method
You’ve now seen numerous DI scenarios and worked your way to many DI
answers (and even one nonanswer). It’s time to put your knowledge to work in the
context of our DI step method. Here’s a rundown of the steps:
Step 1: Get the Specs.
Step 2: Grill the Interrogator.
Step 3: Gather the Data.
Step 4 (if necessary): Power Through.
Why is Step 4 labeled “if necessary”? What does “Grill the Interrogator”
mean? How does the little refrigerator light turn off when you close the door?
All excellent questions! All (except that last one) will be answered right now
as we take a closer look at each step.
Step 1: Get the Specs. You’re familiar with this step from
both the Problem Solving and Quantitative Comparison step methods. The
difference here in DI is that you have to scope out and get a firm handle on the
elements of the diagram(s) before you have any chance of answering the
questions. So, the “specs” in this question type are the parameters of the
graphs or tables presented. You need to perform this step only before the first
question, since the diagrams don’t change from question to question. Issues you
need to notice up front include the following:
- What does the data represent?
- What is the scale of the data presented? Make sure you know how the
things represented in the diagrams are measured. Take note of the units
(thousands, millions, feet, seconds, hours, etc.). If a diagram contains
multiple scales, notice whether they’re the same or different. In tricky DI
sets, multiple scales may be indicated in different units, which makes
eyeballing much more risky.
- If there is more than one diagram, what’s the relationship between
them? Does any obvious correlation emerge? Does one diagram contain
information that represents a subset of the data contained in the other
- Are any trends evident from eyeballing the data? Take a quick look at
the big picture to help you get the gist of the information before moving on
to the first question.
Step 2: Grill the Interrogator. Once you know what the
diagrams are about, it’s time to tackle the first question. Each question
provides a wealth of information that should alert you to the math concepts (if
any) in play and direct you to the data you’ll need to answer it. Grill the
question itself to unearth clues that will lead you in the right direction. When
you know what they’re asking, you’ll recognize what you need to know, which will
further help you determine where you need to look.
Step 3: Gather the Data. By this point, you’ve gotten the
diagrams under your belt and have determined what the question is asking, which
should allow you to venture forth to find the data you need to answer the
question. In some cases you may also need a Math 101 concept to set you on the
right track, but you can get by on many DI questions without “mining the math”
(Step 3 of the PS and QC step methods). You certainly should know how to work
with percentages and be familiar with common data analysis concepts, but overall
you shouldn’t have to dive too deep into your Math 101 knowledge base. If the
question set contains only one diagram, use your information from steps 1 and 2
to direct you to the part of that diagram containing the data relevant to the
question at hand. If the set contains multiple diagrams, then use the
information in the question to tell you where to head, in what order, to get the
numbers you need.
Now, it’s possible you won’t need to “Power Through” in Step 4, which is
why we label this final step if necessary. That’s because the
simpler DI questions test only whether you understand the question asked and can
read the answer right off a graph or table. In those cases, you’ll be done by
Step 3. Questions answered by eyeballing generally fall into this category. More
complex questions, however, require not only that you find the relevant
information but also that you manipulate it after you have it. That’s where Step
4 comes into play.
Step 4 (if necessary): Power Through. If you can’t simply
read the answer off a graph or table, you’ll have to crunch the numbers you
extracted from the diagram(s) in Step 3. You may need to calculate precisely, or
you may get away with approximating. In any case, expect many DI questions to
require at least a bit of work after you’ve gathered your information.
Don’t worry if you’re not totally on top of DI just yet. It’s going to
take practice, more of which awaits you in the practice set at the end of
this chapter and the practice test at the end of the book. But first we’ll
walk you through our step method in the context of another question,
resurrecting one last time our good old home-building scenario.
Price per Square Foot of Exterior
Surface Materials from 1940 to 1990
||If new homes built with siding in 1970
averaged 915 square feet of exterior surface material,
approximately how much money was spent on siding for new
homes in that year?
Step 1: Get the Specs. We’ve seen these diagrams already,
but let’s reiterate the specs for good measure. There are two diagrams, one
graph and one table, each containing siding, brick, and wood information for
six different years. The multipart graph depicts the number of homes built
with each surface material, and the scale is in thousands. We need to be
careful to consider the correct beginning and end points for each segment of
the graph. The note at the bottom eliminates the possibility of
multiple-surface houses, averting possible confusion on that front. The
table contains the prices per square foot of the material in the various
years. Prices generally seem to rise across the years, with one exception in
the wood row.
Step 2: Grill the Interrogator. The question limits its
inquiry to 1970 siding homes, which narrows things down considerably. It
provides the average number of square feet per siding homes built that year
and asks for the approximate amount of money spent on that surface in 1970.
The word approximately and the large difference between the
dollar figures in the choices tell us we can estimate the values to make our
lives easier. That’s a great jump on the question, so let’s move on to Step
Step 3: Gather the Data. We know that money is involved,
so the table will come into play, but what else do we need to know to
calculate the total amount of money spent on siding in 1970? The basic
formula total cost = cost per unit × number of units comes into
play. In this case, number of units is itself broken down
into average number of square feet per house (915, given) and the number of
houses built in that year. So the total siding cost in 1970 = number of
siding houses built in 1970 × 915 square feet per house × cost per square
foot of siding in 1970. The cost per square foot of siding in 1970 is $6.29,
and the number of siding homes built in 1970 was around 8,000. (The siding
segment in that year starts just around 60,000 and ends before the 70,000
Step 4: Power Through. We’ve got our figures, so let’s
bring it on home: Since we’re looking for an approximate value, we can round
915 square feet per house up to 1,000 to make matters simpler. Multiplying
that by 8,000 houses gives us 8,000,000 square feet of siding used for new
homes in 1970. While we’re at it, let’s approximate $6.29 as plain old
$6.00, which gives us 8,000,000 square feet × $6.00 per square foot =
$48,000,000. Is there anything close among the choices? Yup—$46,000,000,
choice D. That number makes sense too, since we rounded 915 up
to 1,000, so we should expect that our answer might skew a bit high, despite
the fact that we also rounded the price down a bit.