Quadratic equation quiz with answer key online. There are several methods for solving quadratic equations one key method being the use of the quadratic formula. Whatever method you use, the outcome is two values of ‘x’. If you substitute any of both values of ‘x’ in the equation, the outcome will always be the same. There are printable tests with answer keys on the worksheets section. Solve these problems for extra practice. This math quiz is free and always online and students can return here at any time of the day. The algebra exercise is for students in 4th, 5th, 6th and 7th grades.