There are two ropes that are equal in length but different in thickness. If you ignite from one end of two ropes, the thin rope will burn out in 40 minutes, and the thick rope will burn out in 120 minutes. If you ignite two at the same time, after a period of time, they will be extinguished at the same time. At this time, there is still 10 centimeters left of the thin rope. It has not burned out, and there is still 30 centimeters of thick rope that has not been burned up. What is the original length of the two ropes in centimeters?
有两条绳子，它们的长度相等，但粗细不同．如果从两条绳子的一端点燃，细绳子40分钟燃尽，粗绳子120分钟燃尽，一次两条同时点燃，经过一段时间后，又同时把它们熄灭，这时量得细绳子还有10厘米没有燃尽，粗绳子还有30厘米没燃尽．这两条绳子原来的长度是多少厘米．
<gadget id="calculator">30 - 10</gadget>
<output>20</output>

<gadget id="calculator">120 / 40</gadget>
<output>3</output>

<gadget id="calculator">3 - 1</gadget>
<output>2</output>

<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<gadget id="calculator">10 * 4</gadget>
<output>40</output>

<result>40</result>