480/120=4, if 60 is subtracted from the dividend, how much should the divisor be subtracted to keep the quotient unchanged.
480/120=4，如果被除数减去60，要使商不变，除数应减去多少．
<gadget id="calculator">480 - 60</gadget>
<output>420</output>

<gadget id="calculator">480 / 420</gadget>
<output>8/7 = around 1.142857</output>

<gadget id="calculator">120 / (8/7)</gadget>
<output>105</output>

<gadget id="calculator">120 - 105</gadget>
<output>15</output>

<result>15</result>