Observe that:
- 17 and 19 are both natural numbers, i.e. [tex] 17,\ 19 \in \mathbb{N} [/tex]
- All natural numbers are integers, and all integers are rationals: [tex] \mathbb{N}\subset\mathbb{Z}\subset\mathbb{Q}[/tex]
- The sum of two natural number is a natural number
So, 17+19 is also a natural number. As such, it is also an integer, and a rational number.
