@ @¶ìÿa@óÝy‹¾a@ u@ @XT . 60 30 [MAΘ 1992]( ) 60 30 . . 1 30 60 . 1×1 = 1 60 30 1800 10 1 = 1 60 6 30 5 . x . 20 6 . .x + 30 1 1800 . x + 30 x + 30 . x = 45 1800 20(x + 30) = 5 1800 6 20x + 600 = 1500 20x = 900 x = 45