A vendor mixed ‘x’ kg of Assam tea costing Rs. 120 per kg with 9 kg of Darjeeling tea costing Rs. 150 per kg. He gained 10% by selling this mixture at Rs. 150 per kg, then value of ‘x’ is?

Total quantity of the mixture = (x + 9) kg ⇒ Cost of ‘x’ kg of Assam tea = Rs. 120x/kg ⇒ Cost of 9 kg of Darjeeling tea = Rs. (9 × 150) = Rs. 1350 ⇒ Total cost of the mixture in Rs. = 120x + 1350 Selling price per kg of the mixture is Rs. = 150 ⇒ Total selling price of the mixture is Rs. = 150(x + 9) Gain percent = 10% ⇒ (Selling price – Cost price) /Cost price × 100% = 10% ⇒ [150(x + 9) – (120x + 1350)] / (120x + 1350) = 1/10 ⇒ 30x/ (12x + 135) = 1 ⇒ 30x = 12x + 135 ⇒ 18x = 135 ⇒ x = 7.5 Kg