The very first test case is wrong. Puzzle description clearly explains that the answer is "1:3" while the answer inside the example AND the test case is "1:2".

# Test case in Bag of Balls is wrong (https://www.codingame.com/ide/puzzle/bag-of-balls)

So the ratio P(A) : P(!A) is 1:2 (read 1 to 2).

I see an explanation, why the answer is 1:2 there.