from functools import reduce


def compute_product_string(product_string):
    """Takes `product_string` and returns the product of the factors as string.

    Arguments:
    - `product_string`: string containing product ('<factor>*<factor>*...')
    """

    factors = [float(f) for f in product_string.split("*")]
    return str(reduce(lambda x,y: x*y, factors))