Math drills aims to improve your mental speed or if you are being lazy it can kick start your brain. Doing these 2-3 times daily will make you faster at math and will keep your brain sharp. There are 3 types of drills-

Arithmetic: Aim is to do 100 questions as fast as possible while maintaining 100% accuracy.
Count to 300: Add the numbers that appear and enter the final number that completes the sum to 300.
Greatest/Lowest: You are supposed to select the greatest or lowest number among 4 choices of numbers.

Questions are carefully designed to not be hard but still keep your brain engaged for few minutes. Try to focus on 100% accuracy for best results.