Number King

This is a Arithmetic game which mentally calculates the numbers of width and height for the limited time of 60 seconds
According to your game level, the numbers can be changed and displayed in a square of 5 x 5.
Let's try to test the ability of the addition for mental arithmetic.

[Random numbers in the level]
Level 0 : 0,1,2,3,4
Level 1 : 0,1,2,3,4,5
Level 2 : 0,1,2,3,4,5,6
Level 3 : 1,2,3,4,5,6,7
Level 4 : 2,3,4,5,6,7,8
...
Level n : n-2, n-1, n, n+1, n+2, n+3, n+4