Activity- statistics problems

Problem 1

If n =10, = 12 and $\sum {x^{2}}=1530findthestandarddeviation$

Solution:

${\frac {\sum x}{n}}={\bar {x}}$

$\sum {x}={{\bar {x}}\times {n}}$

$\sum {x}={12\times {10}}$

$\sum {x}=120$
σ=${\sqrt {{\frac {\sum {x^{2}}}{n}}-({{\frac {\sum x}{n}})^{2}}}}$
σ=${\sqrt {{\frac {1530}{10}}-{144}}}$
σ=${\sqrt {{\frac {1530}{10}}-{144}}}$
σ=${\sqrt {153-144}}$
σ=${\sqrt {9}}$
σ=3

Problem 2

Find the Standard deviation for the following data.

x	03	08	13	18	23
f	07	10	15	10	08

Solution:

x	f	fx	x{^2}	fx
3	7	21	9	63
8	10	80	64	640
13	15	195	169	2535
18	10	180	324	3240
23	8	184	529	4232
	n=50	Σfx=660		Σfx²=10710