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吴卓谦 · 2018年12月08日
问题如下图：
选项：
A.
B.
C.
解释：
答案和解释不符。应该是个减号吧？
Shimin_CPA税法主讲、CFA教研 · 2018年12月08日
答案正确，是减号。看前两行的答案。后面的incorrect answer是常见错误的答案。
10.92% 8.67% C is correct. Correanswer: l(0.30)2(0.10)2+(0.70)2(0.15)2+2(0.30)(0.70)(0.10)(0.15)(−0.70)=0.0009+0.011025−0.00441=0.007515=0.0867=8.67%{l}\sqrt {{{(0.30)}^2}{{(0.10)}^2} + {{(0.70)}^2}{{(0.15)}^2} + 2(0.30)(0.70)(0.10)(0.15)(-0.70)} = \\\sqrt {0.0009 + 0.011025 - 0.00441} = \sqrt {0.007515} = 0.0867 = 8.67\% l(0.30)2(0.10)2+(0.70)2(0.15)2+2(0.30)(0.70)(0.10)(0.15)(−0.70) =0.0009+0.011025−0.00441 =0.007515 =0.0867=8.67% Incorreanswer: l(0.30)2(0.10)2+(0.70)2(0.15)2+2(0.30)(0.70)(0.10)(0.15)(0.70)=0.0009+0.011025+0.00441=0.016335=0.1278=12.78%{l}\sqrt {{{(0.30)}^2}{{(0.10)}^2} + {{(0.70)}^2}{{(0.15)}^2} + 2(0.30)(0.70)(0.10)(0.15)(0.70)} = \\\sqrt {0.0009 + 0.011025 + 0.00441} = \sqrt {0.016335} = 0.1278 = 12.78\% l(0.30)2(0.10)2+(0.70)2(0.15)2+2(0.30)(0.70)(0.10)(0.15)(0.70) =0.0009+0.011025+0.00441 =0.016335 =0.1278=12.78% l(0.30)2(0.10)2+(0.70)2(0.15)2=0.0009+0.011025=0.011925=0.1092=10.92%{l}\sqrt {{{(0.30)}^2}{{(0.10)}^2} + {{(0.70)}^2}{{(0.15)}^2}} = \\\sqrt {0.0009 + 0.011025} = \sqrt {0.011925} = 0.1092 = 10.92\% l(0.30)2(0.10)2+(0.70)2(0.15)2 =0.0009+0.011025 =0.011925 =0.1092=10.92%请问计算错在哪里？得到的是12.78
