There are 30 coins of 1 yuan and 5 cents in Zhang Ming's piggy bank, with a total value of 25 yuan. How many 1 yuan coins are there?
张明的储蓄罐里有1元和5角两种硬币共30枚，总价值25元，其中1元硬币有多少枚．
<gadget id="calculator">1 * 30</gadget>
<output>30</output>

<gadget id="calculator">30 - 25</gadget>
<output>5</output>

<gadget id="calculator">1 - 0.5</gadget>
<output>0.5</output>

<gadget id="calculator">5 / 0.5</gadget>
<output>10</output>

<gadget id="calculator">30 - 10</gadget>
<output>20</output>

<result>20</result>