We can determine, a 30/25/15 series trade discount would be calculated as follows:
let X = retail price.
X - 0.30 × X = Y ⇒ first discounted price.
Y - 0.25 × Y = Z ⇒ second discounted price.
Z - 0.15*Z = T ⇒ total discounted price.
X - 0.30 × X = (1 - 0.30) × X = 0.70 × X = Y
Y - 0.25 × Y = (1 - 0.25) × Y = 0.75 × Y = Z
Z - 0.15 × Z = (1 - 0.15) × Z = 0.85 × Z = T
since Z = 0.85 × Y, then 0.85 × Z = 0.85 × 0.75 × Y
since Y = 0.70 × X, then 0.85 × Z = 0.85 × 0.75 × 0.70 × X
based on the above, then T = total discount
= 0.85 × 0.75 × 0.70 × X
= 0.44625X
30/25/15 series discount is equivalent to a total discount of 44.625%