A restaurant bought 40 kilograms of salt and planned to use it for 80 days, but the actual daily consumption was 0.1 kilogram less than the plan. How many days are these salts actually used?
某饭店买来40千克盐，计划用80天，实际每天比计划少用0.1千克．这些盐实际用了多少天？
<gadget id="calculator">40 / 80</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(1/2) - 0.1</gadget>
<output>0.4</output>

<gadget id="calculator">40 / 0.4</gadget>
<output>100</output>

<result>100</result>