# 1)
from random import randint
a = []
for i in range(100): a.append(randint(1000, 2000))
print(f"1) {len([i for i in range(len(a)) if a[i] % 2 == 0])}\n")

# 2)
from random import randint
a = []
for i in range(100): a.append(randint(1000, 2000))
print(f"2)\n{a}\n")
for i in range(1, len(a), 2):
    first = a[i-1]; second = a[i]
    a[i-1] = second; a[i] = first
print(a)

# 3)
from random import randint
a = []
b = []
for i in range(100):
    x = randint(0, 100)
    if x < 50: a.append(i)
    elif x > 50: b.append(i)
less_than_50 = 0
more_than_50 = 0
for i in a: less_than_50 += i
for i in b: more_than_50 += i
print(f"\n3) Среднее арифметическое:\nБольше 50 - {more_than_50 / len(b)}\nМеньше 50 - {less_than_50 / len(a)}")