An avionics supplier marks up an aircraft sensor by $40\%$ above its manufacturing cost and then offers a trade discount of $15\%$ on the marked price. The net profit percentage earned by the supplier is:

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### 1. Strategy & Theoretical Principles Let cost price be $CP = 100$. - Marked price: $MP = CP \times (1 + 0.40) = 140$ - Selling price after $15\%$ discount: $SP = MP \times (1 - 0.15) = 140 \times 0.85$ ### 2. Analytical Formulation & Calculation $$SP = 140 \times 0.85 = 119$$ Net profit percentage: $$\text{Profit}\% = \frac{SP - CP}{CP} \times 100 = \frac{119 - 100}{100} \times 100 = 19.0\%$$ ### 3. Distractor Forensics - Candidate subtracting percentages directly gets $40 - 15 = 25\%$, forgetting that discount applies to marked price, not cost price. ### 4. Exam Trap & Standard Reference - **Trap Alert:** Discount is always calculated on Marked Price ($MP$), not Cost Price ($CP$). - **Standard Reference:** Aggarwal, R.S., *Quantitative Aptitude*.

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