Every month, a man consumes 20 kg of rice and 8 kg of wheat. The price of rice is 20% of the price of wheat, resulting in a total expenditure of ₹300 per month for rice and wheat combined. If the price of wheat is increased by 20%, what percentage reduction in rice consumption is needed to maintain the same expenditure of ₹300? (Given that price of rice and consumption of wheat is constant.)
- (a)24%
- (b)22%
- (c)40%
- (d)38%
Answer
Why
Correct — C. Let wheat cost w per kg, so rice costs 0.2w.
20(0.2w) + 8w = 300 → 4w + 8w = 300
12w = 300, so wheat = ₹25 and rice = ₹5 per kg
Old split: rice 20 × 5 = ₹100, wheat 8 × 25 = ₹200
Wheat rises 20% to ₹30, and the same 8 kg now costs ₹240
Rice is left 300 − 240 = ₹60, which at ₹5 buys 12 kg
Cut = (20 − 12) ⁄ 20 = 40% → option (c)
Why the others are wrong
- (a)24% — A 24% cut leaves 15.2 kg of rice, costing ₹76. With wheat now at ₹240 the bill is ₹316 — ₹16 over the ₹300 the man must hold to.
- (b)22% — A 22% cut leaves 15.6 kg at ₹78, and ₹240 + ₹78 = ₹318. The rice budget has to fall all the way to ₹60, not merely dip.
- (d)38% — Close, but 38% leaves 12.4 kg costing ₹62, and ₹240 + ₹62 = ₹302. The rice quota is ₹60 exactly, which is a 40% cut.
Concept
Two quantities are held fixed and the stem says so: the price of rice and the quantity of wheat. That makes this a budget split, not a percentage identity.
Recover the two prices from the ₹300 bill, split that bill into a rice part and a wheat part, then let the wheat part swell by 20%. What is left is the new rice budget — and because the rice price has not moved, the quantity falls in exactly the same proportion as that budget.
'The price of rice is 20% of the price of wheat' is a price relation, not a spending one. Rice still ends up at ₹100 of the ₹300 because 20 kg is a large quantity of a cheap grain, and wheat takes the other ₹200.
Key facts
- Wheat works out at ₹25 per kg and rice at ₹5 per kg, which is 20% of the wheat price.
- The original ₹300 splits as ₹100 on rice and ₹200 on wheat.
- A 20% rise lifts the wheat bill from ₹200 to ₹240, leaving ₹60 for rice.
Study next
Common traps
- Cutting rice by 20% because wheat rose 20%, which ignores the sizes of the two budgets.
- Applying the 20% rise to the whole ₹300 instead of to the wheat share alone.
- Reversing the relation and making wheat 20% of the price of rice.
SSC also asks the mirror version, where the consumption cut is given and the change in the bill is wanted.
At 19 Sep 2024, 09:00, Quant Q.17 the tomato price rises 300%, the housewife cuts consumption 70%, and the question is what happens to her expenditure.
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