gives B the number of A's (2/15), then B's (3/5) is equal to A's (3/4), find out how much the original A's number accounts for the sum of A's and B's two numbers.
甲数给乙数甲的(2/15)，这时乙的(3/5)等于甲的(3/4)，求原来甲数占甲乙两数之和的多少．
<gadget id="calculator">20 / 39</gadget>
<output>20/39 = around 0.512821</output>

<result>20/39 = around 0.512821</result>