Each bottle of mineral water in the supermarket sells for 2.5 yuan. Now the supermarket is conducting promotional activities. There are two types of activity plans: ① buy three bottles and get one free; Method ② how much difference.
超市每瓶矿泉水卖2.5元，现在超市搞促销活动，活动方案有2种：①买三瓶送一瓶；②每买满10元减2元，如果要买40瓶矿泉水，买法①和买法②相差多少元．
<gadget id="calculator">40 * 2.5</gadget>
<output>100</output>

<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<gadget id="calculator">40 / 4</gadget>
<output>10</output>

<gadget id="calculator">2.5 / 10</gadget>
<output>0.25</output>

<gadget id="calculator">40 * 0.25 * 2</gadget>
<output>20</output>

<gadget id="calculator">40 - 10</gadget>
<output>30</output>

<gadget id="calculator">30 * 2.5</gadget>
<output>75</output>

<gadget id="calculator">100 - 20 - 75</gadget>
<output>5</output>

<result>5</result>