The distance between the library of Yucai School and the teaching building is 550 meters. Now it is necessary to install a street lamp every 50 meters on the side of the road between the two buildings (neither at both ends). How many street lamps need to be installed on both sides of this road? ?
育才学校的图书馆与教学楼相距550米，现在需要在两栋楼之间的路旁每隔50米装一盏路灯(两端都不装)，这条路的两旁一共需要装多少盏路灯？
<gadget id="calculator">550 / 50</gadget>
<output>11</output>

<gadget id="calculator">11 - 1</gadget>
<output>10</output>

<gadget id="calculator">10 * 2</gadget>
<output>20</output>

<result>20</result>