from typing import List
def all_prefixes(string: str) -> List[str]:
    result = []
    for i in range(len(string)):
        result.append(string[:i+1])
    return result
from typing import List
def mean_absolute_deviation(numbers: List[float]) -> float:
    mean = sum(numbers) / len(numbers)
    return sum(abs(x - mean) for x in numbers) / len(numbers)