编写一个函数，用于计算给定列表中所有元素的平均值，并确保结果保留两位小数。请以 Python 代码形式给出答案。
user
```python
def calculate_average(numbers):
    if not numbers:  # 检查列表是否为空
        return 0.00
    total_sum = sum(numbers)
    count = len(numbers)
    average = total_sum / count
    return "{:.2f}".format(average)

# 示例
numbers = [10, 20, 30, 40, 50]
print(calculate_average(numbers))  # 输出: 30.00
```
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