Calculate drill

Thank you for playing. 1000 downloaded! One character of a formula becomes a blank. The position of a blank is never the same. Mode. 1. 1 digit and 1 digit calculate. Selection from among the four. 2. 1 digit and 1 digit calculate. Direct input. 3. 2 digit and 2 digit calculate. Selection from among the four. 4. 2 digit and 2 digit calculate. Direct input.