A merchant bought 12 desks and 20 stools for Rs. 9600.

Solution

ATQ, Let cost price of 12 desks be Rs. ‘x’ and cost price of 20 stools be Rs. ‘y’. So, x + y = 9600 And 0.25 × x + 0.15 × y = 1800 Or, 0.25 × (9600 – y) + 0.15y = 1800 Or, 0.10y = 600 Or, y = 6000 So, x = 9600 – 6000 = 3600 Cost price of a desk = 3600/12 = Rs. 300 Cost price of a stool = 6000/20 = Rs. 300 Cost price of 6 desks and 12 stools = 300 × 6 + 300 × 12 = Rs. 5400 Desired Percentage = [(7500 – 5400)/5400] × 100 = 38.89%  or ~ 39%