Column solution: Since Xiaodong’s family switched to energy-saving lamps, they only use 4.5 kilowatt-hours of electricity per day, which is 40% less than before. How much electricity did his family use every day?
列式解答：小东家自从换成节能灯后，每天只用4.5度电，比原来节约了40%，他家原来每天用多少度电？
<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (2/5)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">4.5 / (3/5)</gadget>
<output>7.5</output>

<result>7.5</result>