There are 620 ducks in the pond, 120 of them ran away, and 190 of them swam back. How many ducks are there in the pond at this time?
池塘里有620只鸭子，跑走了120只，又游过来190只，这时池塘共有多少只鸭子？
<gadget id="calculator">620 - 120</gadget>
<output>500</output>

<gadget id="calculator">500 + 190</gadget>
<output>690</output>

<result>690</result>