A bridge is 420 meters long, and 21 colorful flags are inserted at equal distances from the beginning to the end on one side of the bridge, and one at each end. How many meters is the distance between each two colored flags?
一座桥全长420米，在它的一侧从头到尾等距离插了21面彩旗，两端各插一面．每两面彩旗之间相距多少米？
<gadget id="calculator">21 - 1</gadget>
<output>20</output>

<gadget id="calculator">420 / 20</gadget>
<output>21</output>

<result>21</result>