折现率计算可以使用计算器第三列来求吗？我列式求出来为什么不对呢？

NO.PZ2016031001000115 问题如下 investor buys a 6% annupayment bonwith three years to maturity. The bonha yielto-maturity of 8% anis currently price94.845806 per 100 of par. The bons Macaulration is closest to: A.2.62. B.2.78. C.2.83. C is correct.The bons Macaulration is closest to 2.83. Macaulration (Macr) is a weighteaverage of the times to the receipt of cash flow. The weights are the shares of the full pricorresponng to eacoupon anprincippayment.Thus, the bons Macaulration (Macr) is 2.83.考点Macaulration解析Macaculay久期就是平均还款期，权重就是现金流现值占总价格的比值。1、第二列CF就是每一期的现金流，分别是6、6和106；2、用折现率8%进行折现到零时刻，就可以得到各期的PV，分别是6/1.08=5.56; 6/(1.08)^2=5.144; 106/(1.08)^3=84.146。将这三个数据加总就是94.85（第三列）；3、权重就是每一个PV占94.85的比例，分别是5.56/94.85=0.0586；5.144/94.85=0.0542; 84.146/94.85=0.88714、最后一列就是第一列perio第四列权重相乘，最终得到M是2.83，故C正确。 为什么要用portfolio 的思路呢？为什么要算每一期权重呢？

NO.PZ2016031001000115 2.78. 2.83. C is correct. The bons Macaulration is closest to 2.83. Macaulration (Macr) is a weighteaverage of the times to the receipt of cash flow. The weights are the shares of the full pricorresponng to eacoupon anprincippayment. Thus, the bons Macaulration (Macr) is 2.83. Alternatively, Macaulration ccalculateusing the following closeform formulMacr={1+rr−1+r+[N×(c−r)]c×[(1+r)N−1]+r}−(t/T)Macr={\{\frac{1+r}r-\frac{1+r+\lbraN\times(c-r)\rbrack}{c\times\lbrack{(1+r)}^N-1\rbrack+r}\}}-(t/T)Macr={r1+r​−c×[(1+r)N−1]+r1+r+[N×(c−r)]​}−(t/T) Macr={1.080.08−1.08+[3×(0.06−0.08)]0.06×[(1.08)3−1]+0.08}−0Macr={\{\frac{1.08}{0.08}-\frac{1.08+\lbrack3\times(0.06-0.08)\rbrack}{0.06\times\lbrack{(1.08)}^3-1\rbrack+0.08}\}}-0Macr={0.081.08​−0.06×[(1.08)3−1]+0.081.08+[3×(0.06−0.08)]​}−0 Macr = 13.50 − 10.67 = 2.83麻烦老师说一下算这个表格里这些数据具体的计算步骤

2.78. 2.83. C is correct. The bons Macaulration is closest to 2.83. Macaulration (Macr) is a weighteaverage of the times to the receipt of cash flow. The weights are the shares of the full pricorresponng to eacoupon anprincippayment. Thus, the bons Macaulration (Macr) is 2.83. Alternatively, Macaulration ccalculateusing the following closeform formulMacr={1+rr−1+r+[N×(c−r)]c×[(1+r)N−1]+r}−(t/T)Macr={\{\frac{1+r}r-\frac{1+r+\lbraN\times(c-r)\rbrack}{c\times\lbrack{(1+r)}^N-1\rbrack+r}\}}-(t/T)Macr={r1+r​−c×[(1+r)N−1]+r1+r+[N×(c−r)]​}−(t/T) Macr={1.080.08−1.08+[3×(0.06−0.08)]0.06×[(1.08)3−1]+0.08}−0Macr={\{\frac{1.08}{0.08}-\frac{1.08+\lbrack3\times(0.06-0.08)\rbrack}{0.06\times\lbrack{(1.08)}^3-1\rbrack+0.08}\}}-0Macr={0.081.08​−0.06×[(1.08)3−1]+0.081.08+[3×(0.06−0.08)]​}−0 Macr = 13.50 − 10.67 = 2.83请问老师表格中perioweight是怎么算出来的

老师我是这样算的您看看对不对 [6/1.08+12/(1.08^2)+(106*3)/(1.08^3)]/94.845806