A box of colored chalks, red chalks account for (9/20) of the box of chalks, blue chalks account for (7/20) of the box of chalks. What percentage of the box of chalks do the red and blue chalks make up?
一盒彩色粉笔，红粉笔占这盒粉笔的(9/20)，蓝粉笔占这盒粉笔的(7/20)．红粉笔和蓝粉笔共占这盒粉笔的几分之几？
<gadget id="calculator">9 / 20</gadget>
<output>9/20 = around 0.45</output>

<gadget id="calculator">7 / 20</gadget>
<output>7/20 = around 0.35</output>

<gadget id="calculator">(9/20) + (7/20)</gadget>
<output>4/5 = around 0.8</output>

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