It took Xiaodong 15 minutes to go from home to school due to the headwind, and 12 minutes to go home from school with the wind. How much did his speed increase when he returned home?
小东从家去学校，由于逆风用了15分钟，从学校回家顺风用了12分钟，回家时的速度提高了多少．
<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">(1/12) - (1/15)</gadget>
<output>1/60 = around 0.016667</output>

<gadget id="calculator">(1/60) / (1/15)</gadget>
<output>1/4 = around 0.25</output>

<result>1/4 = around 0.25</result>