11/15 + 7 ⇒ rational ⇒ the sum of two rationals is always rational
√14+13 ⇒ irrational ⇒ the sum of a rational and an irrational is always irrational
30×√6 ⇒ irrational ⇒ the product of a nonzero rational and an irrational is always irrational
11/12 × 7/15 ⇒ rational ⇒ the product of two rationals is always rational