Master Li makes 50 parts, and the qualified rate of the parts he makes is between 84 and 96%. How many qualified parts does Master Li make at least?
李师傅做50个零件，他做零件的合格率在84～96%之间，李师傅至少做多少个合格的零件．
<gadget id="calculator">84 / 100</gadget>
<output>21/25 = around 0.84</output>

<gadget id="calculator">50 * (21/25)</gadget>
<output>42</output>

<result>42</result>