Xiao Ming went to the store and bought 5 ballpoint pens and several pencils. The price of the ballpoint pen was three times that of the pencil. 2 times, ask him how many pencils he originally wanted to buy?
小明到商店买了5支圆珠笔和若干支铅笔，圆珠笔的价格是铅笔的3倍，当付钱的时候，发现营业员把两种笔的数量互换了，为此他付的钱数是原来的2倍，问他原来想购买多少支铅笔？
<gadget id="calculator">30 - 5</gadget>
<output>25</output>

<gadget id="calculator">3 - 2</gadget>
<output>1</output>

<gadget id="calculator">25 / 1</gadget>
<output>25</output>

<result>25</result>