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A mobile tariff adds the same amount to the bill for every extra minute used. Plotted against the number of minutes, what does the total bill look like?
AA curve that gets steeper as minutes rise
BA curve that flattens off as minutes rise
CA straight line, because the rate stays fixed
DA step that jumps only at whole hours
Answer & Solution
Correct answer: C. A straight line, because the rate stays fixed
1. The tariff adds the same amount for every extra minute, so the rate of change never varies.
2. A rule with a constant rate of change is a linear one, and its graph is always a straight line.
3. A curve would mean the cost per minute was rising or falling as usage grew, which is not what a fixed rate does.
4. So the picture is a straight line, option C.
_Source: OpenStax College Algebra (CC BY 4.0), Ch 4 "Linear Functions", section 4.1 Linear Functions_
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