The idea is a math relay race.

Divide into two (or more depending on number of participants) teams.
Red Team, Blue Team

Once the math problem is introduced the timer starts.

The first student goes to the chalkboard to solve the first math problem as quickly as they can, the teacher yells correct before he can tag the next student in line for the next problem.

The chalkboard is set up by teacher.

Draw a line down the chalkboard to divide in half and put ten problems on the each side.
Once the child has finished the problem and the teacher yells correct the child can erase that problem then run to tag their team mate for the next problem.

Variations:
Boys Team verses Girl Team
Best two out of three, with math problems progressively get harder.

Definitely have prizes for 1st place and 2nd place with a consolation gift for everyone else for trying their best.