During the summer vacation, 6 children make an appointment to make a phone call with each other, how many calls will be made in total?
暑假里，6个小朋友相约互相打一次电话，那么一共要打多少次电话？
<gadget id="calculator">6 - 1</gadget>
<output>5</output>

<gadget id="calculator">5 / 2</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">6 * (5/2)</gadget>
<output>15</output>

<result>15</result>