Each teeth growths from the crown to the root. There are different stages previously described to divide this process, as Crown initiation, one half of the crown, crown complete, root one quarter, root and a half, etc. Each of these stages of each different tooth (incisors, canines, molars, etc) has its own typical age of attainment (years) defined by the mean and the sd.
Incisor 1/4. This stage, defined by the acquisition of one quarter of the root, is attained in modern humans at a mean age of 5.28 years (SD=0.91)
Molar root complete. This stage, defined by the complete root lenght formation of the first molar, is attained in modern humans at a mean age of 8.45 years (SD=1.36).
You can see the normal distribution in the next figure:
Question 1: Which is the probability to find a modern human with these stages in both teeth? The answer must be in the overlapping area below both normal distributions, but I don't remember the procedure to solve it.
Question 2: Imagine we have one individual with an age of 5.5 years. Which is the probability that this individual at this age would have the incisor at that stage (1/4)? And which is the probability this individual would have first molar at stage of Root complete?