On the day of "Six. First" Children's Day, the price of a set of books in Yinchuan Xinhua Bookstore was reduced by 20% to 78.4 yuan. How much is the original price of this set of books?
"六．一"儿童节那天，银川新华书店一套图书降价20%后售价是78.4元．原来这套图书的售价是多少元？
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (1/5)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">78.4 / (4/5)</gadget>
<output>98</output>

<result>98</result>