Let proportions in A, B, and C be \( a, b, c \) with \( a+b+c = 1 \).
Guaranteed return (worst-case) occurs when:
- B falls (\(-3%\)), C rises (\(-2.5%\)), and A yields \( 0.10% \).
Worst-case return = \( 0.001a - 0.03b - 0.025c \).
We want to maximise this subject to \( a+b+c = 1 \).
This is a linear optimisation problem; optimal occurs when worst cases for B and C are balanced across possible market conditions (rise/fall). Solving via equations for equal worst-case in both scenarios yields:
\( a = 0.30, b = 0.32, c = 0.38 \).
Substitute to find guaranteed return ≈ \( 0.15% \), which is higher than \( 0.10% \) from full investment in A.