In the ratio 5:8=15:24, if the former term of the first ratio is added by 1, how much should the latter term be reduced in the second ratio to make the ratio still valid.
在比例5：8=15：24中，如果第一个比的前项加上1，那么第二个比的后项减少多少，才能使比例仍然成立．
<gadget id="calculator">5 / 6</gadget>
<output>5/6 = around 0.833333</output>

<gadget id="calculator">24 * (5/6)</gadget>
<output>20</output>

<gadget id="calculator">24 - 20</gadget>
<output>4</output>

<result>4</result>