A household's electricity bill has a fixed standing charge of \(\pounds 18\) plus a rate of \(\pounds 0.72\) per unit of electricity used. The total bill fo...
Question 1 Report
A household's electricity bill has a fixed standing charge of \(\pounds 18\) plus a rate of \(\pounds 0.72\) per unit of electricity used. The total bill for one month is \(\pounds 86.40\). Letting \(u\) be the number of units used, form and solve an equation to find \(u\). (4)
Answer Details
The total bill is made up of a fixed standing charge plus a rate for every unit of electricity used, so setting up an equation with \(u\) as the number of units used and solving it finds how many units were used that month.
Setting up the equation for the total bill: \(18+0.72u=86.40\). [1 mark]
Subtracting the standing charge from both sides: \(0.72u=86.40-18=68.40\). [1 mark]
Dividing both sides by \(0.72\) isolates \(u\): \(u=68.40\div0.72=95\) units. [2 marks]
Checking the answer: \(18+0.72\times95=18+68.40=\pounds86.40\), which matches the given total bill exactly.
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