A shopkeeper mixes two qualities of tea. The first quality costs ₹150 per kg and is mixed with the second quality in the ratio 4 : 5. If the mixture is sold at ₹130 per kg (at no profit, no loss), what is the cost per kg of the second quality of tea?
- (a)₹100
- (b)₹110
- (c)₹114
- (d)₹120
Answer
Why
Correct — C.
No profit, no loss, so the mixture costs ₹130 per kg.
Take 4 kg of the first and 5 kg of the second: 9 kg in all.
Cost of 9 kg: 9 × 130 = ₹1,170
First quality: 4 × 150 = ₹600
Second quality, 5 kg: 1,170 − 600 = ₹570
Per kg: 570 ÷ 5 = ₹114 → option (c)
Why the others are wrong
- (a)₹100 — ₹100 makes 9 kg cost 600 + 500 = ₹1,100, only ₹122.22 a kg. Selling at ₹130 would then earn a profit, but the stem says no profit, no loss.
- (b)₹110 — ₹110 is the price a 1 : 1 mix would need, since (150 + 110) ÷ 2 = 130. In 4 : 5 the cheaper tea weighs more: 600 + 550 = ₹1,150 for 9 kg, ₹127.78 a kg.
- (d)₹120 — ₹120 makes 9 kg cost 600 + 600 = ₹1,200, or ₹133.33 a kg. Selling at ₹130 would then be a loss, not the no profit, no loss the stem states.
Concept
A mixture's cost per kg is a weighted average of its ingredients' costs, weighted by quantity.
Here 'no profit, no loss' makes the ₹130 selling price equal to that average. So 4 kg at ₹150 and 5 kg at the unknown price must together cost 9 × ₹130.
Alligation gives the same answer: first : second = (130 − x) : (150 − 130). Setting (130 − x) : 20 = 4 : 5 gives 130 − x = 16, so x = ₹114.
Check forwards: (130 − 114) : (150 − 130) = 16 : 20 = 4 : 5.
Key facts
- Mixture cost per kg = total cost ÷ total quantity.
- Alligation: dearer quantity : cheaper quantity = (mean − cheaper price) : (dearer price − mean).
- No profit, no loss means the selling price equals the cost price.
Study next
Common traps
- Assuming the mean sits halfway and answering ₹110, which holds only for a 1 : 1 mix.
- Reversing the ratio, 5 kg at ₹150 with 4 kg of the unknown: 750 + 4x = 1,170 gives ₹105.
15 Sep 2025, 12:30, Quant Q.11 asks for the ratio instead of a price: pulses at ₹60 and ₹90, sold at ₹84 for a 20% profit, cost ₹70 a kg, and (90 − 70) : (70 − 60) gives the keyed 2 : 1.
12 Sep 2025, 09:00, Quant Q.17 does the same with oils at ₹90 and ₹150 sold at ₹144 for a 20% profit: cost ₹120, keyed 1 : 1.
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