Jika x+y =100 dan x/y=1/9, maka y-x=

Bab Bilangan Pecahan
Matematika SMP Kelas VII

x + y = 100
x = 100 - y

x/y = 1/9
9 . (100 - y) = 1 . y
900 - 9y = y
9y + y = 900
10y = 900
y = 900 : 10
y = 90

x = 100 - y
x = 100 - 90
x = 10

y - x = 90 - 10 = 80

x + y = 100......(pers. 1)

x / y = 1/9
y = 9x.............(pers. 2)

Masukkan y = 9x ke pers1
x + y = 100
x + 9x = 100
10x = 100
x = 100/10
x = 10

x + y = 100
10 + y = 100
y = 100 - 10
y = 90

Nilai y - x
= y - x
= 90 - 10
= 80