Data Analysis, Probability, and Statistics
What you need to know
This domain asks you to read tables, bar graphs, line graphs, circle graphs, and scatterplots, and to compute and interpret mean, median, mode, range, and simple probability. You should also recognize trends, make predictions from data, and understand that correlation does not prove causation.
Traps to watch for
- Mean versus median: an outlier pulls the mean but barely moves the median. Questions often ask which measure better represents the data.
- Reading scales: graph axes may start at a value other than zero or jump by 5s or 10s. Check the tick marks before estimating.
- Percent of a total: circle-graph questions usually ask for a count, not the percent. Multiply the percent by the total.
- Probability without replacement: after one item is drawn, both the favorable count and the total drop by one.
- Independent events: multiply probabilities. Mutually exclusive events: add them.
Rule of thumb
For any data question, restate what is being counted and what the total is before computing. Most errors come from using the wrong denominator.
Worked example
A bag holds 4 red and 6 blue marbles. The probability of drawing red, then blue without replacement, is (4/10) × (6/9) = 24/90 ≈ 0.267. With replacement it would be (4/10) × (6/10) = 0.24. The difference is the shrinking denominator.