"cal-coola" challenge :
▷ Work out the exact result, or a close enough one.
▷ The sooner you solve it, the more points you gain.
How to play:
▷ To calculate: Drag tiles into , -, × & ÷
▷ To undo: Double-tap on the tile
▷ To resolve: Drag your computed tile to the target box
The accumulated score after each round is published in Game Center, so you can keep track of the current score of your friends.