Subject: mathqa
Question: jo ' s collection contains us , indian and british stamps . if the ratio of us to indian stamps is 6 to 2 and the ratio of indian to british stamps is 5 to 1 , what is the ratio of us to british stamps ?
Option: 
A: 5 : 1
B: 20 : 2
C: 30 : 2
D: 15 : 2
Answer: C