PBS
Pbs: Solving Linear Inequalities With Negative Numbers
Solve an inequality that has negative numbers and a variable. This video focuses on using inverse operations to solve for a variable and the importance of flipping the inequality when multiplying or dividing by a negative number.
National Council of Teachers of Mathematics
The Math Forum: Ask Dr. Math: Reversing the Inequality Symbol
"Dr. Math" responds to a student inquiry of why it is necessary to reverse the inequality sign when multiplying/dividing by a negative value.