The price of Type A toothbrush is 13.5 yuan for 5 pieces; the price of Type B toothbrush is "buy 5 get 2 free", and the price is 17.5 yuan. Which toothbrush is the cheapest? How much is each cheaper?
甲种牙刷的售价是5支13.5元；乙种牙刷是"买5赠2"，售价是17.5元，哪种牙刷便宜？每只便宜多少钱？
<gadget id="calculator">13.5 / 5</gadget>
<output>2.7</output>

<gadget id="calculator">5 + 2</gadget>
<output>7</output>

<gadget id="calculator">17.5 / 7</gadget>
<output>2.5</output>

<gadget id="calculator">2.7 - 2.5</gadget>
<output>0.2</output>

<result>0.2</result>