Heuristics to highlight

Use suitable numbers; Use equations/algebra.

Is it true that the sum of two rational numbers is always rational? Justify your answer.

Recall that

• a rational number is a real number that can be expressed as $$\frac{a}{b}$$ , where a and b are integers, and $$b\neq0$$ ;
• a real number that is not a rational number is called irrational.

(Source: SMMT for PGDE(Sec) Attempt 1, July 2008.)