If the price of sugar decreases by 20%, then by what percentage must a householder increase her consumption of sugar so as to leave her expenditure on sugar unchanged? 

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RRB Technician Grade III Official Paper (Held On: 29 Dec, 2024 Shift 3)
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  1. \(33\frac{1}{3}\%\)
  2. \(16\frac{2}{3}\%\)
  3. 20% 
  4. 25% 

Answer (Detailed Solution Below)

Option 4 : 25% 
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Detailed Solution

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Given:

The price of sugar decreases by 20%.

Formula Used:

To keep the expenditure unchanged: (Original Price × Original Quantity) = (New Price × New Quantity)

Calculation:

Let the original price be P and the original quantity be Q.

New Price = P - 0.20P = 0.80P

Let increase consumption of sugar = x%

New Quantity = Q + x% of Q = Q(1 + x/100)

Expenditure remains unchanged:

PQ = 0.80P × Q(1 + x/100)

⇒ Q = 0.80Q(1 + x/100)

⇒ 1 = 0.80(1 + x/100)

⇒ 1 = 0.80 + 0.80x/100

⇒ 1 - 0.80 = 0.80x/100

⇒ 0.20 = 0.80x/100

⇒ x = (0.20 × 100) / 0.80

⇒ x = 25%

The householder must increase her consumption of sugar by 25% to keep the expenditure unchanged.

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