F.2 Maths----- Linear Equations in Two Unknown

　x/5 + y/4 =1
　4x + 5y = 20　　[兩邊各乘 20]

　5 - y = x - 1
　　x = 6 - y

Therefore,　4(6-y) + 5y = 20
　　　　　　　　　　y = -4

　　x = 6 - (-4) = 10

5-y = x-1
y = 6-x

x/5+y/4=1
x/5+(6-x)/4=1
20x/5+20(6-x)/4=20
4x+30-5x=20
x=10

y=-4