Question 655395
Mary receives a score of 43 on her chemistry test. The teacher says Mary’s raw test score is equivalent to a z-score of 2.1. Compared to her classmates, how well did Mary do? 
what's the standard deviation?
----
All you can say from that information is that Mary's 43 is 2.1 standard
deviations above the mean.  She did better than normalcdf(-100,2.1) = 98%
of the class.
The information given does not reveal the size of the standard deviation.
=================
Cheers,
Stan H.