Drop enough grains.The shape appears.
Statistics, one idea at a time.
01 / The draw
Thirteen matches.
Win each one.
- 01Data and samplingNot played
- 02Where is the middleNot played
- 03How spread out is itNot played
- 04Probability rulesNot played
- 05Random variables and expected valueNot played
- 06Two variables: covariance, correlation, portfoliosNot played
- 07Counting and the binomialNot played
- 08Poisson: counts per unitNot played
- 09The normal curve and zNot played
- 10Sampling distributions and the CLTNot played
- 11Confidence intervals and sample sizeNot played
- 12Simple regressionNot played
- 13Multiple regressionNot played
- Final: timed closed-book mock, 20 questions0 of 13 won
09
The normal curve and z
The normal is the bell. Any normal becomes the standard one by measuring in SDs from the mean: z = (y − μ) / σ. Then a z table (or NORM.S.DIST) gives the area, and area is probability.
Not played
02 / Labs
Drag the cutoff.
A cafe sells an average of 400 coffees a day, SD 50. How often do you sell more than the cutoff?
P(more than 450 coffees)
15.9%
- z
- (450 − 400) / 50 = 1.00
- How often
- about 1 day in 6
03 / The loop
Learn. Practice. Check.
- 01
Learn
Read the one-line idea, try the example, and drag the lab until the number makes sense.
- 02
Practice
Answer timed questions with fresh numbers. Score 80% on a topic to win its match.
- 03
Check
Misses come back in Due today, and the timed closed-book mock shows how ready you are.
04 / When you’re stuck
Type in the numbers.
Get the work.
05 / Play