Practice Questions
Concept Explanation
When price or consumption changes, total expenditure changes according to both factors. Expenditure = Price × Consumption.
Price Increase, Consumption Same
If price rises by p%, expenditure rises by p% (consumption unchanged).
Compensating Consumption Cut
If price rises by 25%, to keep expenditure same, consumption must fall by 20% (since 1.25 × 0.8 = 1).
Net Expenditure Change
Multiplier = (1 ± price change) × (1 ± consumption change).
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Q1 EasyThe price of rice increases by 20%. If consumption stays the same, expenditure increases by:ExplanationWith unchanged consumption, expenditure changes by the same percentage as price.
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Q2 EasyIf price decreases by 10% and consumption increases by 10%, expenditure changes by:Explanation0.9 × 1.1 = 0.99 → 1% decrease.
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Q3 EasyIf price doubles and consumption halves, expenditure:Explanation2 × 0.5 = 1 → expenditure stays the same.
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Q4 MediumThe price of sugar increases by 20%, by what % should a housewife reduce the consumption of sugar so that expenditure on sugar can be same as before?ExplanationRequired reduction = 20/(100 + 20) × 100 = 16.66%.
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Q5 MediumIf the price of a commodity be raised by 20%, find by how much percent must a householder reduce his consumption of that commodity so as not to increase his expenditure.ExplanationReduction = 20/(100 + 20) × 100 = 16(2/3)%.
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Q6 MediumThe price of a commodity rises from Rs. 6 per kg to Rs. 7.50 per kg. If the expenditure cannot increase, the percentage of reduction in consumption is:Explanation6y = 7.5t → new consumption = 4/5 of original → reduction = 20%.
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Q7 MediumThe price of sugar is increased by 25%. If a family wants to keep its expenses on sugar unaltered, then the family will have to reduce the consumption of sugar by:ExplanationReduction = 25/125 × 100 = 20%.
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Q8 MediumIf the price of sugar decreases by 20%, by what percentage should consumption be increased so that the expenditure on sugar remains the same?ExplanationRequired increase = 20/(100 − 20) × 100 = 25%.
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Q9 MediumPrice rises by 25% and consumption falls by 20%. Net change in expenditure is:ExplanationNet multiplier = 1.25 × 0.8 = 1.0 → no change.
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Q10 MediumA family spends Rs. 4,000 monthly on fuel. If price rises 15% and consumption is unchanged, new spending is:ExplanationNew spending = 4,000 × 1.15 = Rs. 4,600.
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Q11 MediumPrice increases by 10% and consumption by 20%. Net expenditure increases by:Explanation1.1 × 1.2 = 1.32 → 32% increase.
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Q12 HardThe price of a commodity rises from Rs. 9 to Rs. 12.60. If the expenditure does not increase, the percentage of reduction in its consumption is:ExplanationOld quantity for Rs. 9 = 126 units; new quantity = 90 units. Reduction = 36/126 × 100 = 28(4/7)%.
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Q13 HardTo offset a 50% price hike while keeping expenditure unchanged, consumption must be reduced by:ExplanationRequired reduction = 50/(100 + 50) × 100 = 33(1/3)%.
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Q14 HardMonthly grocery bill is Rs. 6,000. After a 10% price rise, consumption is cut by 5%. New bill is:ExplanationNew bill = 6,000 × 1.1 × 0.95 = Rs. 6,270.
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DS1 Easy
An employee tracks fuel costs for a company car. What is the new monthly fuel expenditure?
Statement IThe fuel price per litre rose by 15% this month.
Statement IIThe car's monthly fuel consumption in litres remains the same as last month, when the bill was Rs. 4,000.
ExplanationNew expenditure = 4,000 × 1.15 = Rs. 4,600. Each statement alone is insufficient; together they give the result. -
DS2 Medium
A hostel mess manager wants to keep the monthly grocery bill unchanged after a price hike. By what percent must consumption be reduced?
Statement IThe price of rice per kg has increased by 25%.
Statement IIThe monthly expenditure on rice must remain exactly the same as before the hike.
ExplanationWhen expenditure is fixed, a 25% price rise requires consumption to fall by 25/(100 + 25) × 100 = 20%. Both statements together determine the answer.
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DS3 Medium
A household adjusts both price and quantity after a market change. What is the net percentage change in total expenditure?
Statement IThe unit price of cooking oil increased by 10%.
Statement IIThe family reduced its oil consumption by 5% to control costs.
ExplanationNet multiplier = 1.1 × 0.95 = 1.026 → 2.6% increase. Both the price change and consumption change are needed. -
DS4 Hard
After a price drop, a canteen wants to buy more without overspending. By what percent must consumption increase to keep expenditure unchanged?
Statement IThe price of a commodity decreased by 20%.
Statement IIThe canteen's total spending on that commodity must not change from the previous month.
ExplanationRequired increase = 20/(100 − 20) × 100 = 25%. Statement I gives the price drop; Statement II states the expenditure constraint. Together they fix the answer.