该账户在 40 年末的累计金额是 20 年末账户的累计金额的三倍。
计算 i。
s 20 | ¯ = 3 s 10 | ¯ {\displaystyle {s}_{\overline {20|}}=3{s}_{\overline {10|}}} ( ( 1 + i ) 20 − 1 ) i = 3 ( ( 1 + i ) 10 − 1 ) i {\displaystyle {\frac {((1+i)^{20}-1)}{i}}=3{\frac {((1+i)^{10}-1)}{i}}} ( 1 + i ) 20 − 3 ( 1 + i ) 10 + 2 = 0 {\displaystyle (1+i)^{20}-3(1+i)^{10}+2=0} ( ( 1 + i ) 10 − 1 ) ( ( 1 + i ) 10 − 2 ) = 0 {\displaystyle ((1+i)^{10}-1)((1+i)^{10}-2)=0} ( 1 + i ) 10 = 2 {\displaystyle (1+i)^{10}=2} ( 1 + i ) = 1.07177 {\displaystyle (1+i)=1.07177} i a n n u a l = .035 {\displaystyle i_{annual}=.035}
