To find the average of the observations 10, 20, 65, 102, 108, 115, we need to sum the observations and divide by the number of observations.
The sum of the observations is: $10 + 20 + 65 + 102 + 108 + 115 = 420$
The number of observations is 6. So, the average is: $\frac{420}{6} = 70$
The average of the observations is 70.