That line of thinking breaks down in the real world though.

Its like when some scientist reports they killed 70% of cancer cells in the lab and a news report comes out with scientists develop treatment for 70% of cancer.

You cannot just take "scientist reports they killed 70% of cancer cells in the lab" and then follow-up with a question of "what percent of cancer did the scientist cure?" and then use the only percentage you saw ("70%") as the answer. The information given wasn't not sufficient to answer the question asked; in a test scenario, sure make an assumption but in the real world just get clarification ...