Strength and speed are not enough to fight an invasion of monsters. You have to use your math skills. Besides, they are useful in your real life.
Strike at the sensitive point - correct result of equation. Avoid false results. Control Mathman with the arrows or A, D, W, S. Freeze time using spacebar if necessary (available after three hits in a row).
A context menu should be shown when right-clicking or, on touch devices, long-pressing in the game. This menu especially allows to play in full screen and control the volume.