The dollar-weighted annual yield for this nine-month period is -2.7%.
Solution:
The investment of deposit on April 1 (Feb, March = 2 months)
[tex]\Rightarrow\frac{(9-2)}{9}\times1200=\frac{(7)}{9}\times1200[/tex]
The investment of deposit on May 1 (Feb, March, April = 3 months)
[tex]\Rightarrow\frac{(9-3)}{9}\times1200=\frac{(6)}{9}\times1200[/tex]
Therefore, Dollar-weighted annual yield for this nine-month period,
[tex]\Rightarrow \frac{\text{Total interest}}{\text{Total investments}}[/tex]
On plugging-in the values,
[tex]\Rightarrow\frac{14820-(19800+1200+2600-8400}{19800+\frac{7}{9}(1200)+\frac{6}{9}(2600)-8400}=-0.027[/tex]
In percentage notation,
[tex]-0.027=(-0.027\times100)\frac{1}{100}=-2.7\% (\because \frac{1}{100}=\%)[/tex]