A subtraction formula, the sum of the minuend, the subtrahend and the difference is 1, and the known difference is (3/20), so what is the subtrahend.
一道减法算式，被减数、减数、差三个数加的和是1，已知差是(3/20)，那么减数是多少．
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">3 / 20</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">(1/2) - (3/20)</gadget>
<output>7/20 = around 0.35</output>

<result>7/20 = around 0.35</result>