A school participates in the learning from Lei Feng activity, and each group of 5 people can be divided into several groups; if each group increases to 7 people, it can be reduced to 4 groups. How many people in total participated in the learning from Lei Feng activity?
某校参加学雷锋活动，每组5人，可正好分成若干组；如果每组增加到7人，可以减少4组，一共有多少人参加学雷锋活动？
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 / 7</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">(1/5) - (1/7)</gadget>
<output>2/35 = around 0.057143</output>

<gadget id="calculator">4 / (2/35)</gadget>
<output>70</output>

<result>70</result>