Divide a watermelon into 8 equal portions, mother eats 2 of them, and Xiao Ming eats 3 of them. Please come up with one mathematical problem calculated by addition and one by subtraction, and one by parallel calculation.
把一个西瓜平均分成8份，妈妈吃了其中的2份，小明吃了其中的3份．请你提出用加法和减法计算的数学问题各一个，并列式计算．
<gadget id="calculator">3 / 8</gadget>
<output>3/8 = around 0.375</output>

<gadget id="calculator">2 / 8</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(3/8) - (1/4)</gadget>
<output>1/8 = around 0.125</output>

<result>1/8 = around 0.125</result>