解设这两支蜡烛已燃了x小时1-1/5x=3(1-1/4x)1-1/5x=3-3/4x3/4x-1/5x=211/20x=2x=40/11答这两支蜡烛已燃了40/11小时
(1-x/5)=3(1-x/4)11x/20=2x=40/11(小时)
设点了x小时1-1/5x=3(1-1/4x)1-0.2x=3-0.75x0.75x-0.2x=3-10.55x=2x=40/11小时
L-L/5XT=3(L-L/4T)T=40/11
40/11