signature pen is 8 yuan, and a ballpoint pen is 5 yuan. Xiaohong has 20 yuan. She buys a ballpoint pen and a ballpoint pen. How much money is left? (Answered in two ways?)
一枝签字笔8元，一枝圆珠笔5元．小红有20元钱，她买一枝签字笔和一枝圆珠笔，还剩下多少钱？(用两种方法解答吗？)
<gadget id="calculator">8 + 5</gadget>
<output>13</output>

<gadget id="calculator">20 - 13</gadget>
<output>7</output>

<result>7</result>