Dongdong went to the store to buy stationery, and the money he brought was just enough to buy 10 exercise books or 15 pencils. Now he bought 4 exercise books, how many pencils can he buy with the remaining money?
东东到商店买文具，他带的钱刚好可以买到10本练习本或者15支铅笔．现在他买了4本练习本，剩下的钱还能够买多少枝铅笔？
<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">(1/10) * 4</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (2/5)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">(3/5) / (1/15)</gadget>
<output>9</output>

<result>9</result>