A computer costs 4,000 yuan, and my father bought one at a 20% discount, saving a lot of yuan.
一种电脑售价4000元，爸爸以八折的价钱买了一台，节省了多少元．
<gadget id="calculator">80 / 100</gadget>
<output>4/5 = around 0.8</output>

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

<gadget id="calculator">4_000 * (1/5)</gadget>
<output>800</output>

<result>800</result>