Last year, the number of male teachers in Haicheng Primary School was 2/5 that of female teachers. After transferring 2 male teachers this year, the ratio of male teachers to female teachers is 3:7. How many female teachers are there in Haicheng Primary School?
海城小学去年男教师的人数是女教师的(2/5)，今年调进2位男教师后，男教师与女教师的人数的比是3：7，海城小学女教师有多少人．
<gadget id="calculator">3 / 7</gadget>
<output>3/7 = around 0.428571</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(3/7) - (2/5)</gadget>
<output>1/35 = around 0.028571</output>

<gadget id="calculator">2 / (1/35)</gadget>
<output>70</output>

<result>70</result>