Both A and B live on the same side of a certain street, and the house numbers on this side are all odd numbers. Now it is known that A lives in No. 9, and B lives in No. 191. How many doors are there between the houses of A and B?
甲、乙两人都住某大街的同一侧，这一侧的门牌号码皆是奇数，现已知甲住9号，乙住191号，那么甲、乙两人的住处相隔多少门．
<gadget id="calculator">191 - 9</gadget>
<output>182</output>

<gadget id="calculator">182 / 2</gadget>
<output>91</output>

<gadget id="calculator">1 - 2</gadget>
<output>-1</output>

<gadget id="calculator">91 + (-1)</gadget>
<output>90</output>

<result>90</result>