GRE Quant · Chapter Test
Standard Deviation, Quartiles & Percentiles — 25-Question Test
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Formula Reference Sheet
This chapter
Spread & the empirical rule
| Standard deviation (idea) | typical distance of values from the mean |
|---|---|
| Add constant c to all values | SD unchanged (spread does not shift) |
| Multiply all values by k | SD is multiplied by |k| |
| 68-95-99.7 rule | ≈68% within 1 SD, ≈95% within 2 SD, ≈99.7% within 3 SD of the mean |
Positional measures
| Interquartile range | IQR = Q3 − Q1 |
|---|---|
| Quartiles | Q1 = median of lower half, Q3 = median of upper half |
| kth percentile | the value below which about k% of the data falls |
| Five-number summary (boxplot) | min, Q1, median, Q3, max |
GRE reference
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