In the environmental protection activities of recycling waste batteries, the fourth grade recycled 840 waste batteries, which was 7/8 of the number of waste batteries recycled by the sixth grade, and the number of waste batteries recycled by the fifth grade was 9/10 of that of the sixth grade. How many knots of waste batteries are recycled in the fifth grade?
在回收废电池的环保活动中，四年级共回收废电池840节，是六年级所回收废电池数量的(7/8)，五年级回收废电池的数量是六年级的(9/10)．五年级回收废电池多少节？
<gadget id="calculator">7 / 8</gadget>
<output>7/8 = around 0.875</output>

<gadget id="calculator">840 / (7/8)</gadget>
<output>960</output>

<gadget id="calculator">9 / 10</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">960 * (9/10)</gadget>
<output>864</output>

<result>864</result>