Reading Graphs on the SAT
Some of the math questions on the SAT are called data interpretation. Sounds important, huh? Actually, it’s just a pompous name for “reading a graph,” something you’ve been doing for years.
Don’t let graph problems intimidate you. Here are the three most common types of graphs you’re likely to see on the SAT:
- Bar graph
- Circle or pie graph
- Two-axes line graph
A bar graph has vertical or horizontal bars. The bars may represent actual numbers or percentages. If a bar goes all the way from one side of the graph to the other, it usually represents 100 percent.
Circle or pie graphs
The circle or pie graph represents 100 percent. The key to this graph is determining the total that the percentages are part of. Below the graph you may be told that in 1994, 5,000 students graduated with PhDs. If a 25 percent segment on the circle graph is labeled “PhDs in history,” you know that the number of history PhDs is 25 percent of 5,000, or 1,250.
Two-axes line graphs and scatter plots
A typical line graph has a bottom and a side axis. You plot a point or read a point from the two axes. A special kind of two-axes graph is the scatter plot. A scatter plot contains a bunch of dots scattered around a two-line graph. Here’s an example:
Notice how the points seem to follow a certain trend, going higher as they go to the right. When a trend is present, you can draw a line that estimates the behavior of the points. This line is known as a trend line. On the test, you may be given a scatter plot and have to estimate where the points are going based on the trend line.
Try an example.
- For the following data set,
the trend line has a slope closest to
The correct answer is Choice (A). Because the data points flow downward as they go to the right, it must be Choice (A) or (B). If you look at the top left point, you can estimate its coordinates as (5, 45). The bottom right point is around (20, 15). The slope of the line connecting these points is