John is 31 years younger than his dad. The sum of their ages is 53 years. How many years old is John's dad?
To solve this problem, I need to find a way to relate John's age and his dad's age using algebra. Let me call John's age x and his dad's age y. Then I have two equations: x = y - 31 and x + y = 53. I can substitute x = y - 31 into the second equation and get: y - 31 + y = 53. This simplifies to 2y = 84, so y = 42. This means John's dad is 42 years old. 