If the same blank number is multiplied to each side of a true inequality, the inequality sign is reversed to make the resulting inequality true.

Negative
If the same negative number is multiplied to each side of a true inequality, then the inequality sign flips to make the new inequality true as well

Example:
Take 1 < 5 and multiply both sides by -2 and we get -2 > -10. The "less than" sign flips to "greater than" since -2 < -10 is false. The value of -10 is further to the left of -2 so -10 is smaller in value. The negative basically takes the complete opposite which is why the flip must happen.

This sign flip rule does not happen if you multiply both sides by a positive number.