Flash mental arithmetic

This is a flash mental arithmetic application that allows you to finely adjust the speed, number of digits, number of numbers to add, etc.
You can also customize the color and size of the numbers, background color, etc. to your liking.
You can see the same question over and over again.
I think that this app can be used widely for beginners who are trying flash mental arithmetic for the first time, and for practice for those who aim to win the flash mental arithmetic competition.