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

Let the original price of be N .
? At discount of 20% article costs ? 596
? 596 = (80 x N)/100
? N = (596 x 100)/80
? N = 745
? original price = ? 745

Let amount of electricity bill = ? N
? 4% of N = 13
? (4 x N)/100 = 13
? N = 13 x 25 = ? 325

Here, r₁ = 10 %, r₂ = 20% and r₃ = 30%
? Required discount
= [1 - (1 - r₁/100) (1 - r₂/100) (1 - r₃/100)] x 100%
= [1 - (1 -10/100) (1 - 20/100) (1 - 30/100)] x 100%
= {1 - (9/10) x (4/5) x (7/10)} x 100%
= (1 - 0.504) x 100% = 49.6%

Let the marked price of item = ? N
? {(100 - 14) /100 } of N = 645
? N = (645 x 100)/86 = ? 750

? Marked price of a shirt = ? 320
Discount on a shirt = 320 x 25/100 = ? 80

? Number of shirts has to be purchased to get a rebate of ? 400 = 400/80 = 5