Let the ratio of parts of red pigment and parts of base be
ab.
Herea1=1,b1=8⇒a1b1=18=k (say)Whena2=4,b2=? k=a2b2⇒b2=a2k=418=4×8=32Whena3=7,b3=? k=a3b3⇒b3=a3k=718=7×8=56Whena4=12,b4=? k=a4b4⇒b4=a4k=1218=12×8=96Whena5=20,b5=? k=a5b5⇒b5=a5k=2018=20×8=160
Parts of red pigment1471220Parts of base8325696160