The ratio of the number of students participating in the mathematics competition between A and B schools is 7:8, and the ratio of the number of winners is 2:3. There are 420 students from each of the two schools who did not win the prize, so how many students from the two schools participated in the competition?
甲乙两校参加数学竞赛的人数之比是7：8，获奖人数之比是2：3，两校各有420人未获奖，那么两校参赛的学生共有多少人．
<gadget id="calculator">420 + 420</gadget>
<output>840</output>

<gadget id="calculator">7 - 2</gadget>
<output>5</output>

<gadget id="calculator">7 + 8</gadget>
<output>15</output>

<gadget id="calculator">5 / 15</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 - (1/3)</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">840 / (2/3)</gadget>
<output>1_260</output>

<result>1_260</result>