Only the formula does not count: the paper mill planned to use 420 tons of water in April, but the actual water consumption was 315 tons. What percentage was saved?
只列式不计算：造纸厂四月份计划用水420吨，实际用水315吨，节约了百分之几？
<gadget id="calculator">420 - 315</gadget>
<output>105</output>

<gadget id="calculator">105 / 420</gadget>
<output>1/4 = around 0.25</output>

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