s=1n∑i=1n(bi−1n∑i=1nbi)s = \sqrt{\frac{1}{n}\sum_{i=1}^{n}(b_i -\frac{1}{n}\sum_{i=1}^{n}b_i)}s=n1∑i=1n(bi−n1∑i=1nbi)
⇒\Rightarrow⇒
s=1n∑i=1n(bi−1n∑j=1nbj)2s = \sqrt{\frac{1}{n}\sum_{i=1}^{n}(b_i -\frac{1}{n}\sum_{j=1}^{n}b_j)^2}s=n1∑i=1n(bi−n1∑j=1nbj)2
