Calculate drill

Thank you for playing. 1,000 downloaded!!One character of a formula becomes a blank.The position of a blank is never the same.Mode1. 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.2 digit calculate is difficult. Do you answer correctly?