1 задание.
numbers = [int(input("n%d = " % (x + 1))) for x in range(3)]
print(sum(numbers) / len(numbers))
2 задание.
print(max([int(input("n%d = " % (x + 1))) for x in range(2)]))
3 задание.
n1, n2 = int(input("n1 = ")), int(input("n2 = "))
if n1 >= n2:
print(n1 + n2)
else:
print(n1 * n2)