Answer: 12.6%
Step-by-step explanation:
The bank's expected standard deviation after adding this branch will be calculated thus:
= (Total invested in new branch × Expected rate of return) + (1 - Investment in new branch) × Other assets
= (0.2 × 0.15) + (1 - 0.2) × 0.12
= 0.03 + 0.8 × 0.12
= 0.03 + 0.096
= 0.126
= 12.6%
Therefore, the bank's expected standard deviation after adding this branch is 12.6%.