Shortcut Trick
Overall Selling Price = 30 × 1.10 = Rs. 33/kg.
Equating total SP parts: 8x + 45(x − 8) = 33x
53x − 360 = 33x ⇒ 20x = 360 ⇒ x = 18
Quantity sold at Rs. 45/kg = x − 8 = 18 − 8 = 10 kg.
∴ The correct answer is 10 kg.
Alternate Method
Given:
Cost Price (CP) = Rs. 30/kg, Overall profit = 10%
Quantity sold at Rs. x/kg = 8 kg
Quantity sold at Rs. 45/kg = (x − 8) kg
Formula Used:
Mean SP = CP × (100 + Profit%) ÷ 100
Alligation ratio = (SP2 − Mean SP) / (Mean SP − SP1)
Calculations:
⇒ Mean Selling Price = 30 × 1.1 = Rs. 33/kg
⇒ Using the Alligation ratio: 8 / (x − 8) = (45 − 33) / (33 − x)
⇒ 8 / (x − 8) = 12 / (33 − x)
⇒ 2 / (x − 8) = 3 / (33 − x)
⇒ 2 × (33 − x) = 3 × (x − 8)
⇒ 66 − 2x = 3x − 24
⇒ 5x = 90
⇒ x = 18
⇒ Quantity sold at Rs. 45/kg = 18 − 8 = 10 kg
∴ The correct answer is 10 kg.
Additional Information
Mixtures & Alligation Rule
It allows finding the ratio in which two ingredients at given prices must be mixed to produce a mixture of a desired price: Quantity 1 / Quantity 2 = (Price 2 − Mean Price) / (Mean Price − Price 1).
Profit and Loss Basics
Selling Price (SP) is calculated as CP × (100 + Profit%) ÷ 100. When multiple parts are sold at different prices, the overall SP is the weighted average of the individual SPs.
Replacement Method
When a quantity 'y' is replaced 'n' times from a total mixture 'x', the remaining quantity of the original substance is given by x × (1 − y/x)n.