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Solution

Mean $,\bar x=\dfrac{4.2+4.3+4.0+4.1}{4}=4.15$. Deviations: $0.05,,0.15,,-0.15,,-0.05$. Sum of squares $=0.0025+0.0225+0.0225+0.0025=0.05$. Population variance $,s^2=\dfrac{0.05}{4}=0.0125$. Sample variance $,s^2=\dfrac{0.05}{3}\approx0.0167$.