Passages that fall under the category of Data Representation will require you to be able to quickly interpret a variety of graphs. Data representation passages will include some type of graph or chart, such as a bar or line graph, and you will be expected to establish an understanding of the experiment based on the chart. While you will also have to read tables in Research Summaries passages, this lesson will primarily focus on interpreting the diagrams and charts found in the data representation passages.
In the data representation passages, you will be given a chart or table, along with a brief description, and will be asked various questions based on the information provided in the charts. These types of questions will refer to a single data point on the graph.
Some questions to consider while approaching these types of problems are:
What are the units of measurement?
What are the independent and dependent variables?
Although on the actual ACT you will likely not have enough time to look at each chart in detail, right now this will help us learn how to establish a quick understanding of graphs and charts.
Below is a sample Data Representation passage:
In Table 1, we can see that the independent variable is time (in seconds) and the dependent variable, or what is being measured, is the volume of material A (in cm^3).
Based on the passage, we can see that the volume changes as material A absorbs heat at a rate of 10 calories per second.
In Figure 1, we can see that the independent variable is time (in seconds) and the dependent variable is temperature (in ℃). This figure shows the change in temperature over time of material A. It also indicates the different states of material A. From 0-2 seconds, material A is all liquid. From 2-22 seconds, it is a combination of liquid and gas, and from 22-24 seconds it is all gas.
In Table 2, we can see both the boiling point (in ℃) and the heat absorbed (in cal) of materials B, C, and D. We can relate the boiling points of these materials to the boiling point (the temperature where a substance changes from liquid to gas) of material A in Figure 1. From Figure 1 we can see the boiling point of material A is 10℃.
Now that we have established an understanding of the charts, we can move on to the questions.
The time interval in which the temperature increased the fastest can be determined by where the temperature the temperature rose the most over a set period of time. We can determine this by observing the slopes of the graph.
We can see that temperature increases occur between 0-2 seconds and 22-24 seconds (the temperature is constant between 2-22 seconds). We can see the slope is steeper from 22-24 seconds. We can also calculate the temperature increase in those time frames. Between 0-2 seconds, the temperature increased from -10 to 10, or 20℃. Between 22-24 seconds, the temperature increased from 10 to 50, or 40℃.
Therefore, the fastest temperature increase occurred between 22-24 seconds.
We are trying to determine which material will first turn into a gas, given the same heat absorption rate, atmospheric pressure, and mass. In other words, we want to find which has the lowest boiling point.
From our analysis of the passage and charts above, we know that the boiling point of material A is 10℃. From Table 2, we can see that the boiling point of material B is 13℃, the boiling point of material C is 19℃, and the boiling point of material D is 28℃.
Since material A has the lowest boiling point, it will be the first to be completely turned into a gas. Therefore, the answer is A.