One rainy Thursday, he flipped to a random page. Problem 789: A father is three times as old as his son. In 12 years, he will be twice as old. Find their ages.
Andrei stared at the page. For the first time, the culegere wasn’t asking for a number. It was asking for a reason . He wrote in his notebook: culegere matematica clasa a 9 a
He had learned something the culegere never said out loud: sometimes the right answer is that there is no answer—and explaining why is the real solution. One rainy Thursday, he flipped to a random page
That night, he didn’t stop at three problems. He solved five. Then ten. By December, the blue culegere was battered but beloved. And when his teacher asked the class, “Who enjoys the challenge problems at the end of each chapter?” Andrei raised his hand. Find their ages
He wrote the equations: let son = s , father = f . (f = 4s) (f + 18 = 2(s + 18) \Rightarrow 4s + 18 = 2s + 36 \Rightarrow 2s = 18 \Rightarrow s = 9, f = 36.) Sum = (9 + 36 = 45), which is not prime. A contradiction.