The naughty family of three plans to travel to Mulan Tianchi. If you buy tickets at the ticket office, the adult ticket is 80 yuan, and the student ticket is half price; if you book in advance online, the adult ticket price is 3/4 of the original price, and the student ticket price is also half price. The naughty family of three went to Mulan Tianchi for a trip. How much is it cheaper to book tickets online in advance than to buy tickets at the ticket office?
淘气一家三口计划去木兰天池旅游．如果在售票点购票，成人门票80元，学生票半价；如果在网上提前预订，成人票价是原价的(3/4)，学生票价也是半价．淘气一家三口去木兰天池旅游，在网上提前订票比在售票点购票便宜多少元钱？
<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">1 - (3/4)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">80 * 2 * (1/4)</gadget>
<output>40</output>

<result>40</result>