We need to make units same first. $5$ minutes equal to $300$ seconds. Now we could remove the same unit, second. We get $300:30$ and simplify it to $10:1$. 
What is the simplest form of $5$ minutes $: 30$ seconds? 
Options:
A. $5:30$ 
B. $1:6$ 
C. $6:1$ 
D. $10:1$ 