In a village, (1/3) of the children can swim, (2/3) of the children can ride a bicycle, and (1/7) of the children can both swim and ride a bicycle (of course, it is not necessary to do both at the same time. ). It is known that there are less than 40 children in this village, so how many children are there who can neither swim nor ride a bicycle?
在一个村子里，(1/3)的孩子能游泳，(2/3)的孩子能骑车，并且(1/7)的孩子既能游泳，也能骑车(当然不必同时做两件事)．已知该村的孩子不到40人，那么既不会游泳也不会骑车的孩子有多少人．
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

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

<gadget id="calculator">(2/3) - (1/7)</gadget>
<output>11/21 = around 0.52381</output>

<gadget id="calculator">(1/3) + (11/21)</gadget>
<output>6/7 = around 0.857143</output>

<gadget id="calculator">1 - (6/7)</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">3 * 7 * (1/7)</gadget>
<output>3</output>

<result>3</result>