The cost price of 6 chocolates and 4 biscuits amounts to Rs. 6,960. Additionally, the cost price of 5 chocolates and 7 biscuits totals Rs. 8,880. Each chocolate and biscuit is marked up by 60% and 15%, respectively, and then sold with discounts of d% and Rs. 246, respectively. Despite these variations, the selling price of a chocolate and a biscuit remains the same. What is the value of 'd'?

ATQ, Let the cost price of a chocolate = Rs. ‘x’ Let the cost price of a Biscuits = Rs. ‘a’ ATQ; 6x + 4a = Rs. 6960………………….(1) And, 5x + 7a = Rs. 8880………………..(2) Equation (2) × 6 – Equation (1) × 5, we get (5x + 7a) × 6 – (6x + 4a) × 5 = 8880 × 6 – 6960 × 5 30x + 42a – 30x – 20a = 53280 – 34800 Or, 22a = 18480 Or, a = 18480/22 = 840 Substituting this value ‘a’ in 6x + 4a = 6960 6x + 4 × (840) = 6960 Or, x = {(6960 – 3360)/6} = 3600/6 = 600 So, cost price of a Chocolate and a Biscuits are Rs. 600 and Rs. 840, respectively. Marked price of a Chocolates = 600 × (160/100) = Rs. 960 Marked price of a Biscuits = 840 × (115/100) = Rs. 966 Selling price of a Biscuits = Rs. 966 – 246 = Rs. 720 Therefore discount percentage on a Biscuits = d% = {(960 – 720)/960} × 100 Or, d% = (240/960) × 100 = 25% Or, d = 25