The ratio of number A to number B is 2:5. If number B is reduced by 1, what should be the number of A to keep the ratio constant.
甲数与乙数的比是2：5，乙数如果减少1，要使比值不变，甲数应多少．
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<result>2/5 = around 0.4</result>