Use a red right-angled triangle paper with a hypotenuse of 3 cm, a blue right-angled triangle with a hypotenuse of 5 cm, and a yellow square paper to form a right triangle. What is the sum of the areas of the red and blue triangles?
用一张斜边长3厘米的红色直角三角形纸片，一张斜边长5厘米的蓝色直角三角形纸片，一张黄色的正方形纸片，刚好可以拼成一个直角三角形．红、蓝两张三角形纸片的面积之和是多少平方厘米？
<gadget id="calculator">3 / 2</gadget>
<output>3/2 = around 1.5</output>

<gadget id="calculator">5 * (3/2)</gadget>
<output>15/2 = around 7.5</output>

<result>15/2 = around 7.5</result>