Chapter P, Prerequisites - Section P.2 - Real Numbers - P.2 Exercises - Page 15: 1

a) $4$ b) $-2$ c) $\frac{5}{3}$ d) $\sqrt 2$

a) Natural numbers (counting numbers) are integers $\geq 1$. b) Based on the above definition, we want any integer $\lt 1$ c) A rational number can be expressed as a fraction, but in this case we don't want an integer. c) Any real number that can't be written as a fraction with two integers falls here.