If a pen cost Tk.50 after 10% discount, then what is the actual price or marked price (MP) of the pen?

Question: If a pen cost Tk.50 after 10% discount, then what is the actual price or marked price (MP) of the pen?Solution:Since, we know;MP - D = SP ..................(1) where MP is marked price, D is discount, SP is selling price.Percentage discount, D% = D/MP × 100 ⇒ D = (D% × MP)/100 ........(2)Substitute value of D in (1).MP - (D% × MP)/100 = SP ⇒ MP × (100 - D%)/100 = SPPutting the given values in formulaMP × (100 - 10)/100 = 50 ⇒ MP × (90/100) = 50⇒ MP = (50 × 100)/90∴ MP = 55.55Alternative:SP Tk. 90 when MP Tk. 100∴ SP Tk. 1 when MP Tk. (100/90)∴ SP Tk. 50 when MP Tk. (100 × 50)/90= Tk. 55.55