Two successive discounts of 20% and 20% are equivalent to a single discount of

Given, r₁ = 20% and r₂ = 20%
∴ Single discount equal to r₁ and r₂
= (r₁ + r₂ - r₁ x r₂) / 100 %
= (20 + 20 - 20 x 20) / 100
= 40 - 4 = 36%