Mom goes to a non-staple food store every 4 days, and a department store every 5 days. On average, how many times a week does Mom go to these two stores? (expressed as a decimal)
妈妈每4天要去一次副食商店，每5天要去一次百货商店．妈妈平均每星期去这两个商店几次？(用小数表示)
<gadget id="calculator">9 / 20</gadget>
<output>9/20 = around 0.45</output>

<gadget id="calculator">(9/20) * 7</gadget>
<output>63/20 = around 3.15</output>

<result>63/20 = around 3.15</result>