The day before Christmas, Jia Hui bought 100 greeting cards with 8 cents and 4 cents for 50 yuan, how many cards are there for 8 cents?
圣诞节前一天，嘉慧用50元钱买了8角和4角的贺卡共100张，其中8角的贺卡有多少张．
<gadget id="calculator">100 * 0.8</gadget>
<output>80</output>

<gadget id="calculator">80 - 50</gadget>
<output>30</output>

<gadget id="calculator">0.8 - 0.4</gadget>
<output>0.4</output>

<gadget id="calculator">30 / 0.4</gadget>
<output>75</output>

<gadget id="calculator">100 - 75</gadget>
<output>25</output>

<result>25</result>