In a? symmetric, unimodal? distribution, about? two-thirds of the observations are? where?

In a symmetric distribution, better known as the Gaussian or normal distribution, two thirds of the observations or 66.67% of the observation belongs to the area between the - 3∅ to + 3∅ where ∅ is the standard deviation of the group. it is assumed here that the mean is 1 and the area under the curve is also 1.