def find_average(x):
    return sum(x) / len(x)

med = 0
math = [] #математика
ph = [] #физика
ru = [] # русский
with open ('text.txt', 'r', encoding='utf-8') as f, open ('test.txt', 'w', encoding='utf-8') as f1:
    lines = [line.split() for line in f]
    li = 0 #кол-во строк
    for i in lines:
        for parts in i:
            li+=1 #кол-во строк
            y = parts.split(';') #
            med = [int(y[1]),int(y[2]),int(y[3])] # среднее арифметическое каждого ученика
            a = [int(item) for item in med]
            f1.write(str(find_average(a)) + '\n')
            math += [int(y[1])]
            ph += [int(y[2])]
            ru += [int(y[3])]
    f1.write(' '.join([(str(find_average(math))), (str(find_average(ph))),(str(find_average(ru)))]))