Step 3
CP = 1440/0.8 = Rs. 1800
Verification: 20% of 1800 = 360, so SP = 1800 - 360 = 1440 ✓
Answer: Rs. 1800
Shortcut #3: For successive transactions, multiply factors. 10% profit followed by 20% loss = 1.1 × 0.8 = 0.88, meaning 12% overall loss.
Most Common Trap: Students calculate percentage on Selling Price instead of Cost Price. Remember: Profit% and Loss% are ALWAYS calculated on Cost Price, never on Selling Price. This mistake costs at least 1-2 marks in every exam.
Another frequent error involves sign confusion. When CP > SP, it's a loss situation. When SP > CP, it's profit. Always check this relationship before applying formulas.
Exam Strategy: Start with identifying what's given and what's asked. Write down CP, SP clearly. Apply the basic formula first, then use shortcuts for speed. Double-check by working backwards - if you found CP, calculate SP using the given profit% to verify your answer.