點計 40-50% X =20(方程)

40-50% X= 20

40-0.5X =20

40 =20+0.5X

40-20 =20+0.5X-20

20 =0.5x

20./0.5=0.5X/0.5

X=40

講解：40-50% X =20，當我們遇到減未知數，先把他撥搬到右方，50%X=0.5X。所以變成40=20+0.5X。我們跟着要處理20，我們在左方和右方都-20，就會變成20=0.5X。我們跟住要將0.5X的0.5消滅，我在上方用了除0.5，也可以左方和右方一起乘以2，變成40=X，即X=40

40-50%X=20
40-50%X/50%=20/50%
40-X=20x50/100
40-X=40
40-X+40=40+40
X=80

40-50% X =20
40-20=50%X
20=0.5X
X=40

40-50%x=20
40-50%x+50%x=20+50%x
40=20+50%x
40-20=20+50%x-20
20=50%x
20/50%=x
40=x
x =40

40 - 50%x = 20
40 - 0.5x = 20
40 - 0.5x - 40 = 20 -40
-0.5x/0.5 = -20/0.5
x = 40

Hope I helped =]

40-50% X =20
40=20+50%X
40-20=50%X
20=50%X
40=X

X=40

40-50% X = 20
-50% X = 20-40
-50% X = -20
50% X = 20
X = 20/0.5 = 20 x 2
X = 40