Ratios, Percentages & Data Analysis
Problem-Solving and Data Analysis questions test ratios, percentages, unit rates, and reading/interpreting tables, scatterplots, and basic statistics (mean, median, standard deviation).
Percentages and ratios
Percent change = (new - old)/old × 100%. Watch for 'percent of' vs. 'percent more/less than' — a 20% increase means multiply by 1.20, not just add 20.
For data displays (tables, scatterplots), read the question carefully to identify exactly which row/column/axis is relevant, and whether it's asking for a value, a rate, or a comparison.
Mean is sensitive to outliers; median is not. If a data set's values all increase by a constant amount, the mean and median increase by that same amount, but the standard deviation (spread) stays the same.
Worked Example
A price increases from $80 to $92. What is the percent increase?
- Percent change = (92-80)/80 × 100% = 12/80 × 100%
- = 0.15 × 100% = 15%
Answer: 15%
Key terms (1)
- Percent change
- (new - old)/old × 100%
Practice Quiz
A population of 200 increases by 15%. What is the new population?