A shopkeeper marks an article 40% above cost price. He gives 25% discount and still makes Rs. 20 profit. Find the cost price.
Solution:
Let CP = 100
MP = CP + 40% = 100 + 40 = 140
After 25% discount: SP = 140 × 75/100 = 105
Profit = SP - CP = 105 - 100 = 5
If profit of 5 gives Rs. 20, then CP = 20 × 100/5 = Rs. 400
Worked Example 2: A trader allows 16% discount on marked price and still gains 5%.
If the article costs Rs. 50, what is the marked price?
Solution:
CP = Rs. 50
Gain = 5%, so SP = 50 × 105/100 = Rs. 52.50
Discount = 16%, so SP = MP × 84/100
52.50 = MP × 84/100
MP = 52.50 × 100/84 = Rs. 62.50
Shortcut #3 - Quick MP Calculation: When SP and discount% are known, use MP = SP ÷ (1 - d/100). For 20% discount: MP = SP ÷ 0.8
Most Common Trap: Students confuse discount% base. Discount% is ALWAYS calculated on Marked Price, never on Cost Price or Selling Price.
Many students calculate discount on CP and get wrong answers. Remember: Discount% = (Discount/MP) × 100, not (Discount/CP) × 100.
Another frequent error is in successive discount problems. Students simply add the percentages instead of using the formula.
For 10% and 15% discounts, combined is NOT 25%, but 23.5%.
Practical Tip: When solving discount problems, always identify what is given and what needs to be found. Draw the relationship: CP → MP → SP. Mark the percentages between each step.
This visual approach prevents calculation errors and saves time in exams.