The sixth grade students actively participated in the rope skipping and shuttlecock kicking competitions. Each person participated in at least one of them. 70% of the students participated in the rope skipping competition, and 50% of the students participated in the shuttlecock kicking competition. 12 people participated in both competitions. How many people are in the grade?
六年级同学积极参加跳绳、踢毽子比赛，每人至少参加其中的一项，70%的同学参加了跳绳比赛，50%的同学参加了踢毽子比赛，两项比赛都参加的有12人，六年级共有多少人？
<gadget id="calculator">70 / 100</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">50 / 100</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(1/2) - 1</gadget>
<output>-1/2 = around -0.5</output>

<gadget id="calculator">(7/10) + (-1/2)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">12 / (1/5)</gadget>
<output>60</output>

<result>60</result>