Answer:
55 mg of the vitamin is in the drink.
Explanation:
- Create a proportion based on the word problem. In this case, the proportion is: 
  . .
- Find what you must divide by to get from 100 to 50, which is 2.
- Divide 110 by 2 to solve for x, making the proportion equal.
 , which means 55 mg of the vitamin is in the drink.
, which means 55 mg of the vitamin is in the drink.