Children's Day bookstore to engage in promotional activities. All books in bookstore A will be 25% off, and all books in bookstore B will be "buy four get one free". Teacher Tang wants to buy 10 storybooks with an original price of 20 yuan. Which bookstore is cheaper? How much is it cheaper?
儿童节书店搞促销活动．甲书店所有图书一律七五折，乙书店所有图书一律"买四送一"．唐老师要买10本原价为20元的故事书，到哪家书店买比较便宜？便宜多少元？
<gadget id="calculator">20 * 8</gadget>
<output>160</output>

<gadget id="calculator">75 / 100</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">20 * (3/4)</gadget>
<output>15</output>

<gadget id="calculator">15 * 10</gadget>
<output>150</output>

<gadget id="calculator">160 - 150</gadget>
<output>10</output>

<result>10</result>