Mark is 18 years old. He has a little brother, John, who is 10 years younger. If John and Mark's parents are currently 5 times older than John, how old were they when Mark was born? Let's think first. Chain of thought:
John is 8 years old because 18 - 10 = 8 years old. Their parents are currently 40 years old because 8 * 5 = 40. Therefore, they were 22 when Mark was born because 40 - 18 = 22 years old.
Therefore, the answer is 22.