jika A:b=5:8,maka b-a per a =

a : b = 5 : 8

a = 5b/8
b = 8a/5

(b - a)/a
= (8a/5 - 5b/8)/(5b/8)
= (64a/40 - 25b/40)/(5b/8)
= (64a - 25b)/40 × 8/5b
= (64a - 25b)/25b
= 64a/25b - 25b/25b
= 64a/25b - 1