The father and son started from the starting point of the 100-meter runway at the same time and walked towards the finish line at a constant speed. When the father walked 40 meters, the son walked 30 meters. According to this calculation, when the father reaches the end point, how many meters is the son still away from the end point.
父子俩同时从100米跑道的起点出发，匀速地向终点走去．当父亲走了40米时，儿子走了30米．照这样计算，当父亲走到终点时，儿子离终点还有多少米．
<gadget id="calculator">100 / 40</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">(5/2) * 30</gadget>
<output>75</output>

<gadget id="calculator">100 - 75</gadget>
<output>25</output>

<result>25</result>