Let the ratio of parts of red pigment and parts of base be a/b
Here a₁=1,b₁=8 ⇒ a₁/b₁=1/8=k (say)

When a₂=4,b₂=?
k= a₂/b₂ ⇒ b₂= a₂/k =4/1/8 = 4/8 =32

When a₃=7,b₃=?
k=a₃/b₃ ⇒ a₃=a₃/k = 7/1/8 = 7×8=56

When a₄=12,b₄=?
k=a₄/b₄ ⇒ b₄=a₄/k= 12/1/8=12×8 =96

When a₅=20, b₅=?
k=a₅/b₅ ⇒ b₅ = a₅/k =20/1/8 = 20×8=160

Parts of red pigment 1 4 7 12 20
Parts of base 8 32 56 96 160

Class 8 Maths Chapter 11 Exercise 13.1 Solution in Video

for more answers vist to:
https://www.tiwariacademy.com/ncert-solutions/class-8/maths/chapter-13/