Question Statement:
A watershed has four rain gauge stations $A, B, C, D$ with observed storm rainfall amounts of $40\text{ mm}, 50\text{ mm}, 60\text{ mm}$, and $70\text{ mm}$, respectively. The corresponding Thiessen polygon weightages are $0.20, 0.30, 0.35$, and $0.15$. The average precipitation depth over the watershed in $\text{mm}$ by the Thiessen polygon method is ________ (round off to 1 decimal place).