The original price of a storybook is 20 yuan, and each book is now on sale at a 10% discount. How much can you save by buying a storybook now?
一本故事书原价20元，现在每本打九折出售．现在买一本故事书能省多少钱？
<gadget id="calculator">90 / 100</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">1 - (9/10)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">20 * (1/10)</gadget>
<output>2</output>

<result>2</result>