from fractions import Fraction
p_b = 1 - Fraction(4, 7) * Fraction(3, 6)
p_a_and_b = Fraction(4, 7) * Fraction(3, 6)
answer = p_a_and_b / p_b
assert 0 <= answer <= 1
result = {"conditional_probability": str(answer), "eligible_pairs": 30, "favourable_pairs": 12}
import json
print(json.dumps(result, ensure_ascii=False, sort_keys=True))