Twenty-sixth Amendment to the United States Constitution
In Oregon v. Mitchell, the Supreme Court looked at whether the voting age changes that Congress added to the Voting Rights Act were constitutional.  This means they looked at whether the changes agreed with the rules in the Constitution, or broke them.  The judges on the Supreme Court strongly disagreed with each other in this case.  Eventually, five out of the nine judges agreed on a decision - just enough to reach the majority needed for a decision.  However, most of the judges did not agree on which legal reason was behind their decision.