During the "June 1st" period, Xinhua Bookstore held a "buy four, get one free" activity. Mr. Liu paid 80 yuan for buying 20 of the same storybooks. What is the original price of each storybook?
"六•一"期间，新华书店举行"买四赠一"活动，刘老师买20本同样的故事书共付80元，每本故事书原价多少元．
<gadget id="calculator">20 / 5</gadget>
<output>4</output>

<gadget id="calculator">20 - 4</gadget>
<output>16</output>

<gadget id="calculator">80 / 16</gadget>
<output>5</output>

<result>5</result>