A kind of exercise book, the original price is a yuan per book, after the price is increased by 10%, the price is reduced by 10%, how much is each book now.
一种练习本，原来每本a元，提价10%后，又降价10%，现在每本是多少元．
<gadget id="calculator">10 / 100</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">1 + (1/10)</gadget>
<output>11/10 = around 1.1</output>

<gadget id="calculator">1 - (1/10)</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">(11/10) * (9/10)</gadget>
<output>99/100 = around 0.99</output>

<result>99/100 = around 0.99</result>