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The standard deviation is a measure of the spread of a set of data. To calculate the standard deviation of a sample, we first need to calculate the mean (average) of the data. For the sample 2, 3, 5, and 6, the mean is \(\frac{2 + 3 + 5 + 6}{4} = 4\).

Next, we need to calculate the variance, which is the average of the squared differences between each data point and the mean. For each data point, we subtract the mean and square the result. Then we add up all these squared differences and divide by the number of data points. The variance for this sample is \(\frac{(2 - 4)^2 + (3 - 4)^2 + (5 - 4)^2 + (6 - 4)^2}{4} = \frac{4 + 1 + 1 + 4}{4} = \frac{10}{4} = \frac{5}{2}\).

Finally, to get the standard deviation, we take the square root of the variance: \(\sqrt{\frac{5}{2}}\).

So, the standard deviation of the sample 2, 3, 5 and 6 is \(\sqrt{\frac{5}{2}}\).