GRE Quant · Chapter Test
Distributions & the Normal Curve — 25-Question Test
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Formula Reference Sheet
This chapter
Reading a distribution
| Relative frequency | (frequency of a value) / (total count) |
|---|---|
| Cumulative frequency | running total of counts up to a value |
| Mean of a frequency table | Σ(value × frequency) / Σ(frequency) |
The normal curve (memorise)
| Within ±1 SD of the mean | ≈ 68% of the data |
|---|---|
| Within ±2 SD | ≈ 95% |
| Within ±3 SD | ≈ 99.7% (nearly all) |
| Each half is symmetric | mean = median = mode; 50% on each side |
| z-score (standardised value) | (value − mean) / standard deviation |
Correlation
| Correlation coefficient r | always between −1 and +1 |
|---|---|
| Positive / negative / none | r > 0 up-trend, r < 0 down-trend, r ≈ 0 no line |
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