Chapter 2 - Solving Linear Inequalities - 2.2 - Solving Inequalities Using Addition or Subtraction - Exercises - Page 65: 23

Inequality : $x-9\lt 4$ Solution : $x\lt 13$

Let the number is $x$. Difference of $x$ and $9$ is $x-9$. Difference is fewer than $4$. The inequality is $\Rightarrow x-9\lt 4$ Add $9$ to each side. $\Rightarrow x-9+9\lt 4+9$ Simplify. $\Rightarrow x\lt 13$