During the Spring Festival, 10 children agree to make a call every two children, and how many calls should be made.
春节期间，10个小朋友约定每两个小朋友通话一次，要通多少次电话．
<gadget id="calculator">10 - 1</gadget>
<output>9</output>

<gadget id="calculator">9 / 2</gadget>
<output>9/2 = around 4.5</output>

<gadget id="calculator">10 * (9/2)</gadget>
<output>45</output>

<result>45</result>