BlitzCalc

BlitzCalc is a free, open-source calculator game that will test your mental math. It's just like any other calculator except you can't enter any numbers more than 1 digit long with the keypad. Rely on 5 operators and your wits to get the calculator's output to the number specified as fast as possible!

Featuring 70 global scoreboards in race mode and a no-pressure practice mode with 3 difficulty settings, BlitzCalc is sure to help just about anybody improve their mental math.

This app optionally uses Google Play Game Services for achievements and leaderboards.