Xiao Ming and his father are climbing the stairs. There are 60 steps in total, Dad climbs 3 steps per step, and Xiao Ming climbs 2 steps per step. Ask how many steps are there that neither Xiao Ming nor his father have climbed?
小明和爸爸进行登台阶运动．台阶共有60级，爸爸每步登3级，小明每步登2级．问小明和爸爸都没有登过的台阶有多少级？
<gadget id="calculator">60 / 2</gadget>
<output>30</output>

<gadget id="calculator">60 / 3</gadget>
<output>20</output>

<gadget id="calculator">60 / 6</gadget>
<output>10</output>

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

<gadget id="calculator">30 + 10</gadget>
<output>40</output>

<gadget id="calculator">60 - 40</gadget>
<output>20</output>

<result>20</result>