The number A is A, which is B less than the number B (4/5). What is the formula to express the number B with letters?
甲数是A，它比乙数的(4/5)少B，用字母表示乙数的式子是多少．
<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<result>4/5 = around 0.8</result>