Li Ming bought 4 math books for 3 yuan, and there is 2 jiao left over. What is the unit price of the math books?
李明用3元钱买了4本数学本，还余下2角，数学本的单价是多少．
<gadget id="calculator">3 - 0.2</gadget>
<output>2.8</output>

<gadget id="calculator">2.8 / 4</gadget>
<output>0.7</output>

<result>0.7</result>