Xiao Ming bought 5 exercise books for 4.50 yuan, and 5 grid books for 2.50 yuan. How much is each exercise book more expensive than each grid book?
小明买了5本练习本用了4.50元，5本方格本用了2.50元．每本练习本比每本方格本贵多少元？
<gadget id="calculator">4.5 / 5</gadget>
<output>0.9</output>

<gadget id="calculator">2.5 / 5</gadget>
<output>0.5</output>

<gadget id="calculator">0.9 - 0.5</gadget>
<output>0.4</output>

<result>0.4</result>