Shortcut Trick
Use the direct proportionality formula: (Quantity1 × SP%1) / Price1 = (Quantity2 × SP%2) / Price2
Where SP% = 100 − Loss% or 100 + Profit%.
⇒ (90 × 70) / 1557 = (n × 118) / 708
⇒ 6300 / 1557 = 118n / 708 ⇒ n = (6300 × 708) / (1557 × 118)
⇒ n = (6300 × 6) / 1557 = 37800 / 1557 ≈ 24
∴ The correct answer is 24.
Alternate Method
Given:
⇒ Selling Price (SP1) of 90 pens = ₹1557
⇒ Loss percentage = 30%
⇒ New Selling Price (Total) = ₹708
⇒ Desired Profit percentage = 18%
Calculations:
⇒ Cost Price (CP) of 1 pen = 1557 / (90 × 0.70)
⇒ CP of 1 pen = 1557 / 63 = 519 / 21 = ₹(173/7)
⇒ Required Selling Price (SPper pen) for 18% profit = (173/7) × (118 / 100)
⇒ SPper pen = (173 × 118) / 700 = 20414 / 700 ≈ ₹29.16
⇒ Number of pens to be sold for ₹708 = 708 ÷ SPper pen
⇒ Number of pens = 708 ÷ (20414 / 700)
⇒ Number of pens = (708 × 700) / 20414 = 495600 / 20414 ≈ 24.27
⇒ Taking the nearest integer value based on standard transaction units:
∴ The correct answer is 24.
Additional Information
Basic Profit and Loss Relation
Selling Price (SP) = Cost Price (CP) × (100 ± Profit or Loss %)/100. This is the fundamental relation used to switch between CP and SP.
Price and Quantity Inverse Rule
When the total expenditure or revenue is constant, the Quantity of items is inversely proportional to the Price per item. n1 × P1 = n2 × P2.
Combined Proportionality
In problems involving changing rates and changing total values, use: (Price1) / (Quantity1 × Rate1) = (Price2) / (Quantity2 × Rate2).