每个方程先简化0.9x-y=2/3(x-y)⇒7/30x-1/3y=0⇒7x-10y=0......〔1〕0.8x-50-y=1/4(x-y)⇒11/20x-50=3/4y=0⇒22x-30y=2000......〔2〕〔1〕×3+〔2〕得x=2000y=1400
