Question 25
Khang and his grandfather have the following ages. In $2010$, the grandfather’s age was $k$ times Khang’s age, where $k$ is a natural number. Some years later, the grandfather’s age was $5$ times Khang’s age. In $2023$, it was $4$ times Khang’s age, and the grandfather was younger than $100$. Find $k$.
Model clarification: ages are positive whole numbers at the same annual reference date. The intermediate five-times event also occurs at such a date, an integer number of years after $2010$.
Model clarification: ages are positive whole numbers at the same annual reference date. The intermediate five-times event also occurs at such a date, an integer number of years after $2010$.