This page is part of my unofficial solutions manual to the GRE Paper Practice Book (2e), a free resource available on the ETS website. They publish the questions; I explain the answers. If you haven’t worked through the Practice Book, give Section 5 a shot before reading this!

5.17: Median Gas Tax

This is the first problem in the “chart block,” which is like Reading Comprehension for math. The questions in this subsection tend to involve lots of arithmetic and some basic statistics (esp. mean and median). You may also need to employ some simple word-problem algebra, but the emphasis here is on using the charts to find the data requested, then performing simple calculations on that data.

In most cases, the chart block will include two charts or graphs of different kinds. It could be a bar graph and a pie chart (as it is here), or a table and a scatter plot, or some other combination. In any case, an important preliminary step for each question is to figure out which chart(s) are relevant. Easier problems will use data from only one of the charts on the page, but in harder problems, you’ll need to synthesize or compare data from both.

In 5.17, we have it relatively easy: the problem stem itself instructs us to look at the bar graph. There are an odd number of countries represented, so to find the median, all we need to do is arrange the values in order:

{24.1%, 40.0%, 56.9%, 62.0%, 67.6%, 70.0%, 70.7%, 72.7%, 76.8%]

The median, which corresponds to answer choice (A), is underlined above.

In fact, we don’t even need to write down a separate list, because the graph is drawn to scale. Instead, we can read the graph from left to right, stopping when we reach the fifth of the nine values. (On the GRE, data graphics like the ones here are always drawn to scale, as are coordinate planes and number lines. Other geometric figures, however, are not necessarily drawn to scale — a point we’ll revisit in later questions.)

Math Review Reference

For more on this topic, see the following sections of the GRE Math Review:

• 4.1: Graphical Methods for Describing Data (pp. 61-64)
• 4.2: Numerical Methods for Describing Data (p. 69)