A 280-page story book, Xiaohong read 20% on the first day and 30% on the second day, how many pages are left?
一本280页的故事书，小红第一天看了20%，第二天看了30%，还剩多少页没看？
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">1 - (1/5) - (3/10)</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">280 * (1/2)</gadget>
<output>140</output>

<result>140</result>