Where in the world did you learn stats from? You would be correct if we were talking about a standard normal distribution with mean 0 and standard deviation 1.

Where in the world did you learn stats from? You would be correct if we were talking about a standard normal distribution with mean 0 and standard deviation 1. Very different. In the case of mean 100 and standard deviation ~15 or so, the probability of two samples being at least 10% different is very small like under 1%.