Mom spent a total of 6.4 yuan calling grandma for a total of 16 minutes. How much did she spend on average per minute?
妈妈给奶奶打电话一共花了6.4元，共通话16分钟，平均每分钟花多少钱？
<gadget id="calculator">6.4 / 16</gadget>
<output>0.4</output>

<result>0.4</result>