Question
The price of electricity rose by 40%. Ravi, in response,
reduced his usage by 25%. Determine the change in his electricity bill.Solution
ATQ,
Let initial electricity cost be Rs. 100a and usage be 100b units
Initial bill = 100a × 100b = Rs. 10000ab
New bill = (1.40 × 100a) × (0.75 × 100b) = Rs. 10500ab
Required percent = [(10500ab - 10000ab) ÷ 10000ab] × 100 = 5% increase
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