If the profit percent got on selling an article is numerically equal to its cost price in rupees and the selling price is Rs. 39, then cost price (in Rs.) will be- यदि एक वस्तु को बेचने पर प्राप्त प्रतिशत लाभ का संख्यात्मक मान इसके क्रय मूल्य के बराबर है और विक्रय मूल्य 39 रू. है तो क्रय मूल्य (रू. में) होगा-

Let CP = x rupees. Given profit% = x (numerically equal to CP). Profit% = (Profit/CP) × 100 = (SP - x)/x × 100 = x. So (39 - x)/x × 100 = x. Solving: (39 - x) × 100 = x^2, so x^2 + 100x - 3900 = 0. Using quadratic formula: x = [-100 + √(10000 + 15600)]/2 = [-100 + √25600]/2 = [-100 + 160]/2 = 30. (Negative root rejected as CP > 0). Verification: CP=30, SP=39, Profit=9, Profit% = (9/30)×100 = 30%, which equals CP numerically.