Explanation:Symmetrical distribution occurs when the values of variables appear at regular frequencies and often the mean, mode, and median all occur at the same point. If a line were drawn dissecting the middle of the graph, it would reveal two sides that mirror one other.It is that type of frequency curve, for which mean = median = mode, figure (a).The skewed distribution is also called asymmetrical distribution. For this type of frequency distribution mean, median and mode do not have the same value. Skewness is + ve or ” ve depending upon the location of the mode with respect to the mean.In a positively skewed distribution, there is a long tail on the right and the mean is on the right of the mode (Fig. (b)).In a negatively skewed distribution, there is a long tail on the left and the mean is on the left of the mode (Fig. (c)).Hence, The curves that occur for a distribution in which class frequencies go on decreasing symmetrically on either side of the central value are called symmetrical curves.