Make a platter for every two kinds of fruits, how many different platters can be made with 4 different fruits.
每两种水果做一个拼盘，用4种不同的水果可做多少种不同的拼盘．
<gadget id="calculator">4 - 1</gadget>
<output>3</output>

<gadget id="calculator">3 / 2</gadget>
<output>3/2 = around 1.5</output>

<gadget id="calculator">4 * (3/2)</gadget>
<output>6</output>

<result>6</result>