Five years ago, the sum of Sebastian's age and his sister's age was 3/4 of their father's age. How old is their father today if Sebastian is 40 years old and 10 years older than his sister? Let's be accurate as possible.
If Sebastian is 40 years old and 10 years older than his sister, his sister is 40 - 10 = 30 years old. Five years ago, Sebastian was 40 - 5 = 35 years old. Similarly, Sebastian's sister's age was 30 - 5 = 25 years old. The sum of their ages five years ago was 25 + 35 = 60. Five years ago, the sum of Sebastian's age and his sister's age was 3 / 4 of their father's age, meaning their father's age was 60 / 3 / 4 = 80 years. The father's age is now 80 + 5 = 85.
The answer: 85.