Mini lesson
Contrapositives
For “if A, then B,” the valid counterpart is “if not B, then not A.” Reverse and negate; do not simply reverse the rule.
Original practice library
Smart drills.
Choose one skill, focus on the reasoning, then review your result. Each drill opens in its own practice page.
Mini lesson
Necessary vs. sufficient
A necessary condition is required for an outcome. A sufficient condition guarantees it. “If admitted, then oriented” does not mean every oriented student is admitted.