Final answer:
The oldest sister is 63 years old. This was found by creating equations based on the information given about the sisters' ages and then solving for the youngest sister's age first.
Step-by-step explanation:
Let's denote the youngest sister's age as 'y'. According to the problem, the oldest is three times the youngest (3y), the second oldest is two years younger than the oldest (3y - 2), the middle sister is twice as old as the youngest (2y), and the fourth sister is three years older than the youngest (y + 3). Adding up their ages gives us the equation y + 3y + (3y - 2) + 2y + (y + 3) = 211.
Simplifying, we have 10y + 1 = 211. Subtracting 1 from both sides gives 10y = 210. Dividing both sides by 10 yields y = 21, which is the youngest sister's age. Therefore, the oldest sister is three times the youngest, which means her age is 3 × 21 = 63 years old.