def num_mines(score):
    if score < 5:
        num_mines = 10
    if 10 <= score <50:
        num_mines = 20
    if 50 <= score <75:
        num_mines = 30
    if 75 <= score <100:
        num_mines = 40
    #else:
        #num_mines = 50
    return num_mines