TI 36X Pro data pair limit...

[Csaba Tizedes]

...and for the single variable measurement, just calculate Student t-values divided by SQRT(number of measured data points). You will get something this:

Code:

================================================================================​=====
Number of measured data (n):            2      3      4      5      6      7      8
    Degrees of freedom (df):            1      2      3      4      5      6      7
================================================================================​=====
Two sided probability   (P): 0.95 |  8.98   2.48   1.59   1.24   1.05 | 0.92   0.84
                                  |                     +-------------+
Two sided probability   (P): 0.90 |  4.46   1.69   1.18 | 0.95   0.82   0.73   0.67
                                  |              +------+
Two sided probability   (P): 0.85 |  2.95   1.32 | 0.96   0.80   0.69   0.62   0.57
================================================================================​=====

And you can see clearly, if you want to reduce the variance of the measured data, you must to make at least n=7 measurement for two-sided probability P=0.95 and n=5 for P=0.90 (and n=4 for P=0.85).

Of course, this is not reflecting your exam-score example, because that is a measurement of 15+ independent variable and your professor generated from these measured values one property (the limit of acceptable score), and my example is about when you measures ONE variable 5-7-9... times. It is must to understand the difference. In your case it is required to collect AND store data if you want to draw the limit and later want to separate the measured values, but in my case this is not required. In my case the data collection purpose is increasing the reliability (decreasing variance).