Xiaobing was sloppy in doing the questions. He regarded the 9 in the tens digit of the addition calculation problem as 7, and the 7 in the hundreds digit as 1. The total number of mistakes was 291. What should be the correct number?
小兵做题较马虎，将加法计算题的十位9看作7，百位7看成1，错得总数291，正确的得数应是多少．
<gadget id="calculator">700 - 100</gadget>
<output>600</output>

<gadget id="calculator">90 - 70</gadget>
<output>20</output>

<gadget id="calculator">291 + 600 + 20</gadget>
<output>911</output>

<result>911</result>