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Question

The price of rice is increased by 25%. By what percent should a family decrease its consumption so that their expenditure remains the same?

This question was previously asked in
RRB NTPC 2019 CBT 1 Question Paper (8-Mar-2021) (Shift 2)
The correct answer is
20%

Price Increase Calculation

Let the original price of rice be $P$ and the original consumption be $C$. The original expenditure is given by the formula: $ \text{Expenditure} = \text{Price} \times \text{Consumption} $ So, the original expenditure is $E = P \times C$.

New Price and Constant Expenditure

The price of rice is increased by 25%. The new price, $P'$, can be calculated as: $ P' = P + 0.25 \times P = P(1 + 0.25) = 1.25P $ The family wants to keep the expenditure the same. Let the new consumption be $C'$. The new expenditure $E'$ must equal the original expenditure $E$. $ E' = P' \times C' $ $ E = E' \implies P \times C = 1.25P \times C' $

Consumption Decrease Percentage

To find the new consumption $C'$, we rearrange the equation:

$ C' = \frac{P \times C}{1.25P} $ $ C' = \frac{C}{1.25} $ Since $1.25 = \frac{125}{100} = \frac{5}{4}$, we have: $ C' = \frac{C}{5/4} = \frac{4}{5}C = 0.8C $

The decrease in consumption is $C - C'$:

$ \text{Decrease} = C - 0.8C = 0.2C $

To find the percentage decrease in consumption, we use the formula:

$ \text{Percentage Decrease} = \frac{\text{Decrease in Consumption}}{\text{Original Consumption}} \times 100\% $ $ \text{Percentage Decrease} = \frac{0.2C}{C} \times 100\% $ $ \text{Percentage Decrease} = 0.2 \times 100\% = 20\% $ Therefore, the family should decrease its consumption by 20%.

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