甲：√(30-21)^2x0.3+(20-21)^2x0.5+(10-21)^2x0.2
=√(9^2x0.3+1x0.5+121x0.2)
=√(81x0.3+1x0.5+121x0.2)
=√(0.1x(81x3+5+121x2))
=√(0.1x(243+5+242))
=√0.1x490
=√49
=7
乙：根号里面（50-26)^2x0.3+(20-26)^2x0.5+(5-26)^2x0.2
=24^2x0.3+6^2x0.5+21^2x0.2
=0.1X(24^2x3+36x5+21^2x2)
=0.1x(576x3+180+441x2)
=0.1x(1728+180+882)
=0.1x2790=279
√279=16.7032930约等于16.7
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