A tradesman gives 4% discount on the marked price and gives 1 article free for buying every 15 articles and thus gains 35%. By how much % more is the marked price above the cost price? ​ Give full explanation

Let the MP of 1 article = Rs 1

MP of 15 article = Rs 15

SP of (15+1) articles = 15 x 96/100

= Rs 14.40

CP of 16 article = 14.40/135 x 100

= Rs 32/3

CP of 1 article = 32/3x16

= Rs 2/3

Required % = 1/3 x 3/2 x 100

= 50