In welchem Verhältnis steht
... German for what is the ratio of ... to ... (externer Link)
German: In welchem Verhältnis steht die 10 zur 5? Antwort: 2
English: What is the ration of 10 to 5? Answer: 2
In colloquial English (outside the maths classroom) people often use between-and rathter than of-to:
Mathematical English: What is the ratio of boys to girls in this class?
Colloquial English: What is the ration between boys and girls in this class?