A shopkeeper has two types of pulses: one costing ₹60/kg and the other costing ₹90/kg. He mixes them in a specific ratio and sells the mixture at ₹84/kg, thereby earning a 20% profit. In what ratio did he mix the two types of pulses?
- AOption (a)
1:3
- BOption (b)
2:1
- COption (c)
3:2
- DOption (d)
4:1
View answer & explanationHide answer & explanation
Correct answer
2:1
Why this answer is correct
Shortcut Trick
Mean Cost Price (CP) = SP × [100 ÷ (100 + Profit%)] = 84 × (100 ÷ 120) = ₹70/kg.
By applying the rule of alligation on the Cost Prices:
Ratio = (CP of Type 2 − Mean CP) : (Mean CP − CP of Type 1)
Ratio = (90 − 70) : (70 − 60)
Ratio = 20 : 10 = 2 : 1
∴ The correct answer is 2:1.
Alternate Method
Given:
Cost price of Type 1 pulse = ₹60/kg
Cost price of Type 2 pulse = ₹90/kg
Selling price of the mixture = ₹84/kg
Profit on selling = 20%
Formula Used:
Cost Price (CP) = Selling Price (SP) × [100 / (100 + Profit%)]
Alligation Ratio = (Dearer CP − Mean CP) : (Mean CP − Cheaper CP)
Calculations:
⇒ Mean CP of the mixture = 84 × [100 / (100 + 20)]
⇒ Mean CP = 84 × (100 / 120) = ₹70/kg
Type 1 Type 2 ₹60 ₹90 Mean CP ₹70 90 − 70 70 − 60 20 10 Ratio = 20 : 10 = 2 : 1
⇒ Using the alligation rule:
⇒ Ratio of Type 1 to Type 2 = (90 − 70) : (70 − 60)
⇒ Ratio = 20 : 10 = 2 : 1
⇒ Alternate algebraic check: Let x kg of Type 1 and y kg of Type 2 be mixed.
⇒ 60x + 90y = 70(x + y)
⇒ 90y − 70y = 70x − 60x
⇒ 20y = 10x ⇒ x : y = 2 : 1
∴ The correct answer is 2:1.
Additional Information
Alligation Rule
It is a mathematical rule to determine the ratio in which two ingredients at given prices must be mixed to produce a mixture of a desired average price. Ratio = (Dearer Price − Mean Price) : (Mean Price − Cheaper Price).
Cost Price vs Selling Price
The rule of alligation must always be applied on equivalent values. If applying on prices, always use the Cost Price (CP) for all components including the mean value, never directly on Selling Price if a profit/loss percentage is involved.
Replacement Method
If from a vessel containing 'a' units of pure liquid, 'b' units are drawn off and replaced by water 'n' times, the remaining pure liquid is calculated as: Remaining = a × (1 − b/a)n.