import re


def remove_numbers(tweet):
    """
    Replaces all numbers in a tweet with the word
    'number'.
    INPUT:
        tweet: original tweet as a string
    OUTPUT:
        tweet with all numbers removed
    """
    words = re.split(r'\s+', tweet)
    new_words = []

    for word in words:
        if bool(re.search(r'\d', word)):
            new_words.append('number')
        else:
            new_words.append(word)

    return ' '.join(new_words)