There are 40 students in Class 1 of June. Some (3/4) students have subscribed to "Primary School Students' Mathematics Journal", and some (4/5) students have subscribed to "Primary School Students' Chinese Learning". How many people have subscribed to both?
六1班有40人，有(3/4)的同学订了《小学生数学报》，有(4/5)的同学订了《小学生语文学习》，两种都订的至少有多少人？
<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">(4/5) - 1</gadget>
<output>-1/5 = around -0.2</output>

<gadget id="calculator">(3/4) + (-1/5)</gadget>
<output>11/20 = around 0.55</output>

<gadget id="calculator">40 * (11/20)</gadget>
<output>22</output>

<result>22</result>