The number of A is (7/8), the number of B is (4/7) of the number of A, what is the number of B.
甲数是(7/8)，乙数是甲数的(4/7)，乙数是多少．
<gadget id="calculator">7 / 8</gadget>
<output>7/8 = around 0.875</output>

<gadget id="calculator">4 / 7</gadget>
<output>4/7 = around 0.571429</output>

<gadget id="calculator">(7/8) * (4/7)</gadget>
<output>1/2 = around 0.5</output>

<result>1/2 = around 0.5</result>