The distance between two telephone poles is 30 meters, and 5 trees are planted equidistantly in the middle, so how many meters is the distance between the second tree and the fourth tree?
两根电线杆之间相距30米，中间等距离地栽了5棵树，那么第2棵树到第4棵树之间相距多少米．
<gadget id="calculator">5 - 1</gadget>
<output>4</output>

<gadget id="calculator">30 / 4</gadget>
<output>15/2 = around 7.5</output>

<gadget id="calculator">4 - 2</gadget>
<output>2</output>

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

<result>15</result>